Big Sur Upgrade not Enough Free Space = Serious Issue & Possible Data Loss! UPDATED

The macOS Big Sur upgrade is not checking to make sure enough free HD space is available. The upgrade will start, then run out of space and fail. If FV2 encryption is enabled, you will be locked out of your data!

UPDATED 10/07/21 Latest Updates!!!For the latest information be sure to check the UPDATES section below.

Quick Summary – When you start the macOS Big Sur upgrade, the installer should first check to make sure your Mac has enough free space available. If the installer finds that you do not have enough free space for the upgrade, it will stop and not let you continue. You should see a pop up message showing you how much space is needed before you can attempt the upgrade again. This free space check is NOT working. The upgrade will start even if you only have 1% of free space left and will fail. Your hard drive is now 100% full and the installer is now stuck in a boot loop attempting to finish the install. This leaves you unable access your data! I will go over all the details below and show you a fix at the end.

I’ve been trying to get a handle on this issue for over a month now. The first signs that this is becoming a larger issue came after the macOS Big Sur 11.2 update was made available. Reports started to roll in saying that the Big Sur Upgrade failed and the only way to fix it was to erase and reinstall macOS. I noticed an increase in traffic to this article. >

https://mrmacintosh.com/reinstalling-big-sur-on-apple-silicon-macs-with-11-0-20a2411-error/

The reason behind the traffic increase was because the M1 personalization error message was very close to the new error.

Big Sur Upgrade out of space error = An error occurred preparing the software update.

Big Sur Upgrade out of space error = An error occurred applying the software update.

Apple Silicon M1 personalization error = An error occurred preparing the update.

This led me to investigate this issue further.

Mr. Macintosh Full report and Deep Dive into the issue + Multiple fixes and workarounds to save your data and let the Big Sur Update finish!

Past macOS update issues like this one

This isn’t the first time I’ve reported on update issues that could cause data loss. The 2019-001 Security update issue was close to this one. If you installed the 2019-001 Security Update and the Mac was encrypted, the user could be locked out.

Security Update 2019-001 update causing data loss on some T2 Mac computers mrmacintosh.com/mojave-2019-001-security-update-causing-data-loss-if-interrupted/

Table of Contents

  • 1. Big Sur 11.2 Upgrade not enough free space problem.
  • 2. Affected Big Sur full installers
  • 3. Are the Big Sur Updaters also affected? (example 11.1 > 11.2 delta update)
  • 4. Affected Mac Hardware
  • 5. How can I tell if my Mac is affected by this issue?
  • 6. How can I prevent this from happening to me?
  • 7. User Reports
  • 8. Reproducing the issue
  • 9. What happens when the upgrade installer runs out of space?
  • 10. FileVault = Data locked out ?
  • 11. Can I get my Mac out of this install loop?
  • 12. You have 2 different options for fixing this issue.
  • 13 How to fix this issue + retain your data!
  • 143. How to fix this issue – Erase & Reinstall macOS
  • 15. This is a serious problem.
  • 16. If you are seeing this issue, please contact Apple.
  • 17. Credits

UPDATES!

UPDATE – 10/07/21 – If you are finding this article, it is most likely because you have Upgraded from macOS Mojave to Big Sur or installed the latest Big Sur 11.6 update. Your Mac no longer boots, it gets stuck at the progress bar. This is a brand NEW issue that is happening. DO NOT ERASE YOUR DATA, it is all still there if you don’t have a backup. I am working on an article now to show you how to recover your data before you reinstall macOS.

UPDATE – 05/02/21 – The Big Sur Upgrade out of space issue should be gone by now. This issue was fixed in the 11.3 installer.

UPDATE – 03/17/21 – Users are still having this issue, I’ve updated the error message section to add –

UPDATE – 02/19/21 – I’ve heard from you! I just finished an update video that goes over how to connect your Big Sur problem Mac to a Catalina & Big Sur Host Mac via Target Disk Mode! You no longer need a High Sierra or Mojave Mac. I also go over how to boot to an external USB drive that has macOS on it to fix the issue. Finally I walk you through a new way to fix your Mac if you do NOT have a 2nd Mac using Internet Recovery!

UPDATE – 02/15/21 – Apple has just released a new build of macOS Big Sur 11.2.1 (20D75). I’ve confirmed that the new installer has fixed the not enough space check!!!

Apple just released macOS Big Sur 11.2.1 (20D75) that fixes the out of space error.

2/14/21

UPDATE #3 – 02/14/21 – In some tests and including the demonstration in my video, I was able to get Macintosh HD to mount (in Big Sur) on the desktop after entering in the password for TDM. (I can’t remember if this was my T2 Unencrypted test or not). If you see “Macintosh HD” Mounted on your desktop, you can do the following. Open disk utility and right click on “Macintosh HD – Data” and click “Show In Finder”. Your Data volume should mount!

UPDATE #2 – 02/14/21 – A new way to mount an Encrypted Mac to a Big Sur or Catalina Device. (Previously this would only work on a Mojave or High Sierra Mac). You can use Disk Utility on Big Sur to erase “Macintosh HD” System Volume ONLY. Doing this will then allow you to mount “Macintosh HD – Data” and your password will now work! You can either backup your data, or clear some space. The upgrade is still staged and can finish if you don’t want to do a full erase. I go over this process at the very end of the video. The article instructions will be updated soon.

UPDATE #1 – 02/14/21 – Just finished my video on this issue, it ended up being over one hour long. The video is one of the most detailed videos that I’ve ever produced. I went over the entire issue, plus went over how to fix the issue in a step-by-step set of instructions. I had to go over multiple situations that a user might be in. This is a very complicated issue and I did my best to try and explain it. I hope you find it helpful.

PREVIOUS UPDATES

UPDATE 02/13/21 – I now have a new way to rescue your Mac if it’s encrypted so you do not need a Mohave or High Sierra Mac. I am putting together that information now. You will be able to use a catalina or Big Sur Mac. I also just finished filming my deep dive video on this issue. I’ll will walk you through how to fix this issue step-by-step. I’m editing it now, stand by.

UPDATE 02/12/21 – I’ve added a new section below on how to rescue your data when your Mac is FileVault encrypted. This new way will work if you do not have a 2nd Mac for Target Disk mode, or if your Mac is newer and you can’t install Mojave on it. The new way involves installing macOS Mojave from recovery on an external USB drive. Once installed you can boot to that external drive and remove enough files from “Macintosh HD – Data” for the Big Sur Upgrade to finish.

UPDATE 02/11/21 – I’ve updated the Affected Big Sur Installers section.

1. Big Sur 11.2 Upgrade not enough free space problem.

What are the reported problems with this update?

  • 1. Big Sur Upgrade stuck in an install loop
  • 2. Stuck in recovery Boot Recovery Assistant. Pop up error – An error occurred preparing the software update – An error occurred applying the software update
  • 3. Big Sur Recovery startup disk screen that shows blank = no startup disk available.

2. Affected Big Sur full installers

This issue affects the following macOS Big Sur Installers. I’m checking with the downloadable Big Sur full installer application.

  • 1. Big Sur 11.3 Beta – Confirmed
  • 2. Big Sur 11.2 – Confirmed
  • 3. Big Sur 11.1 – Not affected
  • 4. Big Sur 11.0.1 – Not affected

3. Are the Big Sur Updaters also affected? (example 11.1 > 11.2 delta update)

I wanted to make sure the issue was only happening with the Big Sur Upgrade and not the point release updates. First I ran a few tests on an 11.1 system. Then I downloaded the 11.2 delta update and then filled the hard drive with a large dmg file. Next, I attempted to kick off the update and luckily software update stopped me. I cleared up 1.5GB and the updater let me install the update but did NOT finish. Instead of getting stuck in an update loop the Mac just booted back into OS. I increased the free space to 2.5GB and the update finished properly.

Attempting to update from Big Sur 11.1 to 11.2 with only 500MB free space.

4. Affected Mac Hardware

In the past, macOS update problems could only happen on specific hardware. Not this time around. If you installed the macOS Big Sur Upgrade on a compatible Mac and did not have enough free space, you will have problems.

2018-2020 Mac devices with a T2 security chip make things even more difficult if you enabled Filevault 2 encryption.

The differences are between 2018+ T2 Macs and FileVault encryption. If you have a T2 Mac, you will not be able to get into macOS recovery because your password will not work. This problem further complicates recovery efforts.

Even more frustrating, unless you disabled external boot security you will not be able to boot to a USB Big Sur installer or external hard drive.

NOTE: Apple Silicon Macs are immune to this issue because the minimum OS M1 Macs can run is macOS Big Sur. I guess it could be possible, if you attempted to run the full installer over the top of your current install.

More on recovery my efforts below.

5. How can I tell if my Mac is affected by this issue?

If you installed the macOS Big Sur Upgrade and you are now stuck in boot loop ending with the error – An error occurred preparing the software update – you are affected by this issue. The other error that you might get is “An error occurred applying the software update.”

This is the error you will see after trying to upgrade to macos Big Sur. An error occurred preparing the software update.

6. How can I prevent this from happening to me?

Apple states that you need the following amount of free space available for a Big Sur upgrade.

 If upgrading from macOS Sierra or later, macOS Big Sur requires 35.5GB of available storage to upgrade. If upgrading from an earlier release, macOS Big Sur requires up to 44.5GB of available storage.

https://support.apple.com/kb/sp833

https://support.apple.com/kb/sp833

So you need at least a minimum of 35.5 GB for the Big Sur Upgrade.

It’s unknown if the size calculation includes the 13GB full installer or not.

EDIT: Steve said that the 35GB number does NOT include the 13GB Big Sur Installer.

If you are on macOS Sierra or later and have 35.5GB free space, the Big Sur upgrade will complete successfully.

7. User Reports.

Some of the very first reports of this issue started to roll in November of last year!

This issue is NOT new and sadly users have been dealing with this for months. Some have lost all data due to this problem. At the time the only way to fix this was a full erase and reinstall of macOS.

https://discussions.apple.com/thread/252038616?answerId=253922337022

I tried to do the Big Sur update and near the end of the installation i get the message. Then i’m asked to select a startup disk. I’ve tried rebooted a few times and it always happens. I assume i’ll need to do a recovery of some sort.

Apple Discussions Forum user

https://www.reddit.com/r/applehelp/comments/k9q0a8/big_sur_update_not_working/

 Tried updating to Big Sur on my Macbook Air. It has given me the error when it comes close to finishing saying “an error occurred preparing the software update” it then gives me two windows one saying choose startup disk and a macos update assistant that both never load. I have tried to fix this but no fix has worked for me yet, including holding down options and opening a disk boot screen and choosing the macintosh hd disk, which still didn’t end up working for me

Reddit User

8. Reproducing the issue

When trying to figure out an issue like this, reproducing the issue is critical. If you can figure out the exact steps needed to trigger the issue, sometimes a workaround can be found. Most of the time, reproducing an issue like this is easier said than done.

This time around, I was able to reproduce the issue. The first time I saw a screenshot of the error, it looked like a failed install. In this situation, the issue could be anything!

When the Big Sur 11.2 update was made available, reports started to increase. I started to look further into this issue and found out that many users are experiencing this problem.

Hard drive free space available!

MacAdmin stevemaser mentioned he was seeing some weirdness when he was testing Big Sur upgrades. He noticed inconsistencies from the installer from when he needed to start the upgrade.

Could not having enough free HD space be the cause of the “An error occurred preparing the software update” error?

It’s time to find out.

I ran some tests on the upgrade process using the macOS Big Sur 11.2 installer.

  • Scenario #1 Free space = less than 13GB
  • 1. Installer will error out (before starting the upgrade) because it doesn’t have enough free space to transfer the upgrade files to a temporary location.
  • Scenario #2 Free space = less than 15GB
  • 1. Installer now has enough space to transfer the needed files to a temporary location. The upgrade will start (when it should give an error) and reboot to the installer and fail. Your Mac is now stuck in an install loop.

BINGO we are now able to reproduce the issue! Next, let’s try to figure out what is happening during the upgrade process.

9. What happens when the upgrade installer runs out of space?

After the the installer restarts your Mac, it still needs free space for the upgrade. Depending on how full your hard drive is, the install could crash out quickly or much later in the install.

macOS Big Sur Upgrade attempting to finish.

The installer will upgrade files on your hard drive until it reaches 100% capacity attempting to finish the upgrade. When that happens, the installer will silently error out and restart. Your Mac will now boot to a recovery type environment called “Boot Recovery Assistant”

This is the Boot Recovery Assistant environment and the error that you will see. An error occurred preparing the software update.

Boot Recovery Assistant is not a full macOS recovery environment. You can only click ok on the error. After clicking OK you will be shown a progress bar that says macOS Update Assistant and the select a startup disk menu.

macOS Update Assistant

You can then attempt to close the progress bar window or click the choose startup disk menu.

Choose Startup Disk menu – Macintosh HD is missing!

The problem is, startup disk does not show your hard drive. All you can do at this point is shut down or restart from the Apple Menu. When you restart the entire process will start over again in a never ending loop.

10. FileVault = Data locked out ?

Why is the upgrade issue so serious when FileVault encryption is enabled?

Your account password is not accepted in any of the normal recovery prompts.

  1. Recovery
  2. Target Disk Mode (Catalina & Big Sur)

If FileVault is enabled on macOS Catalina and Big Sur, you will be prompted to enter in your admin password before getting into recovery.

Your password is NOT accepted for recovery.

When you enter in your password here it will not work even though the password is correct.

If you try to reset your password with a Personal Recovery Key or AppleID, the password reset the process will fail.

Attempting to reset your password will fail, your only option is to restart. This will start the upgrade loop again.

If you can’t get into recovery, you can’t troubleshoot or access your files.

Target Disk Mode will not work on Catalina and Big Sur. The password is not accepted even though it works to unlock your mac to start the upgrade.

The password IS accepted in TDM in macOS Mojave and High Sierra. Why will it only work in 10.14 and 10.13? I’m not totally sure. It might be due to the changes in APFS or the dual drive layout.

Investigation

I attempted everything I could think of to free up space, figuring if I could maybe I could unlock the disk in TDM. This is what I could see over TDM.

The encrypted drive was 100% full and could not be unlocked.
The partition view of the encrypted full drive.

My first attempt was to power down during the upgrade process. This worked in freeing up some space (12GB to be exact).

Capacity In Use By Volumes:   466936836096 B (466.9 GB) (93.4% used)

Sadly, this did not work and I could still not unlock the drive.

I moved to attempting unlock the drive in terminal.

diskutil apfs unlockVolume /dev/disk3s5 -user test Passphrase: Unlocking the specific cryptographic user test on APFS Volume disk3s5

Error unlocking APFS Volume: Malformed UUID (-69578)

Yikes

Could I erase the Macintosh HD partition, or any other partition that was not Macintosh HD – Data?

diskutil eraseVolume APFS Drive /dev/disk3s5 Started erase Preparing to erase APFS Volume content Checking mount state Erasing APFS Volume disk3s5 by deleting and re-adding Deleting APFS Volume from its APFS Container Unmounting disk3s5 Erasing any xART session referenced by 128F46B9-D251-4CD1-8036-146EC457EA4E Deleting Volume

Error: -69623: Unable to delete the given APFS Volume and remove it from its APFS Container

Nope. I figured it would not be possible to remove a volume from an encrypted container, but we are in desperate times I had to try!

Maybe I could remove the temporary update volume?

sudo diskutil apfs deleteVolume /dev/disk3s5 Started APFS operation Deleting APFS Volume from its APFS Container Unmounting disk3s5 Erasing any xART session referenced by 128F46B9-D251-4CD1-8036-146EC457EA4E Deleting Volume

Error: -69623: Unable to delete the given APFS Volume and remove it from its APFS Container

11. Can I get my Mac out of this install loop?

The answer is YES! but the explanation is a little complicated.

You are most likely in one of the following scenarios.

  1. 2013-2017 Mac – FileVault 2 Encryption Not Enabled
  2. 2013-2017 Mac – FileVault 2 Encryption Enabled
  3. 2018-2020 Mac – FileVault 2 Encryption Not Enabled
  4. 2018-2020 Mac – FileVault 2 Encryption Enabled

Why 4 different situations? It comes down to the built in protection of macOS recovery when your Mac has FileVault 2 Encryption enabled. The other problem is the built in boot security of T2 Mac computers. T2 Mac systems are shipped with external boot disabled. This means you will not be able to use a USB installer or external hard drive to help rescue the Mac. Let’s go over how to fix this issue.

12. You have 2 different options for fixing this issue.

Now that we know the different situations, let’s go over how to fix the issue.

Do you need to save or retain your data?

If the answer is YES > 12. How to fix this issue and retain my data.

If the answer is NO > 13. How to fix this issue – Erase and Reinstall.

13. How to fix this issue + retain your data!

This section is divided into 2 parts. Part one is for if your Mac is encrypted with FileVault 2. The 2nd section is for if your Mac is not encrypted.

FileVault 2 Enabled

When FileVault is enabled on macOS Catalina or Big Sur, you are required to enter your account password before entering macOS recovery. This is critical because the only way to recover (retain user data) a FileVault enabled Mac will be with the help of a 2nd Mac.

If your Mac is encrypted and you need to recover your data, you have 2 options. One with just your mac and a USB Drive and the other with a 2nd Mac and a Thunderbolt or USB Cable using Target Disk Mode.

Option #1 – Install macOS Mojave on a external USB, SD Card or Hard drive.

  1. You can boot from this external version of macOS. This will allow you to clear enough space from “Macintosh HD – Data”
  2. Use an external USB flash drive or external hard drive. You install macOS on an external USB, SDCard or hard drive. Once Mojave is installed from recovery to the external drive boot to it by holding down Option after reboot. Once booted to mojave, you will see your drives on the desktop. You can then mount “Macintosh HD – Data” from Disk Utility. Now you can delete files from the “Macintosh HD – Data” then reboot. The Big Sur upgrade will finish.

Option #2 – 2nd Mac Required – Target Disk Mode

  1. You need a 2nd Mac running macOS High Sierra or Mojave. (Big Sur & Catalina Mac fix instructions coming soon)
  2. One of the following cables are required. USB-C to USB-C 3.0 Cable, or a ThunderBolt 3 Cable.
  3. Once you have the target Mac in Target Disk Mode, you can use the host mac running 10.14 or 10.13 to mount the disk after entering your encryption password. > https://support.apple.com/guide/mac-help/transfer-files-mac-computers-target-disk-mode-mchlp1443/mac
  4. As soon as you plug in your cable from the target mac to the host mac, you will get a pop-up window asking you to enter the password for your problem Mac.
You will see this popup once connected to Target Disk Mode on the host Mac.

5. After entering your password, 3 volumes should mount on your desktop.

The volume that holds your data is Macintosh HD – Data. Open this volume and then navigate to your home folder.

Your home folder mounted via target disk mode.

You can now remove any extra files so you can get under the 20-30GB needed to finish.

click on Macintosh HD – Data – then press command I you can now see how much free space is left on the drive.

DON’T FORGET TO EMPTY THE TRASH BEFORE REBOOTING.

Once you have deleted enough files, you can shut down and unplug the target mac from your host Mac. Power it back on and it should now finish the Big Sur Upgrade!

FileVault 2 Not Enabled

If you did not enable FileVault encryption, recovery is a little easier. We can help the macOS Big Sur Installer finish by clearing up some free space! Since we are not prompted for a password to enter macOS recovery, we can delete files in the following ways.

If you only have your Mac

  1. Remove files via terminal.app in macOS recovery.
  2. 2013-2017 Macs (or 2018-2020 if you enabled External boot in the recovery security settings) – Use an external USB flash drive or external hard drive. You install macOS on an external usb, SDCard or hard drive. Once installed boot to that external drive. You will see your drives on the desktop, you can then mount “Macintosh HD – Data” from Disk Utility. You can then delete files from the “Macintosh HD – Data” then reboot. The Big Sur upgrade will finish.

If you have a 2nd Mac

  1. Boot Mac to Target Disk Mode. You can use a 2nd mac to mount your troublesome Mac HD on the desktop. You can now remove files. Follow the detailed instructions in #12 above.

14. How to fix this issue – Erase and Reinstall.

If you have a confirmed backup or just do not need any data on your Mac, you can erase and reinstall macOS.

This is pretty straight forward. If you have a 2013-2017 Mac, you can just boot to recovery, erase the drive and reinstall macOS

If you have a 2018-2020 T2 Mac with FileVault 2 enabled, you will need to perform a “Erase Mac”.

The “Erase Mac” option when you can’t get into recovery.

You can follow the instructions here > https://support.apple.com/en-us/HT211983

15. This is a serious problem.

The fact that this problem is still in macOS Big Sur 11.3 Beta means the issue has been occurring unchecked for months.

Losing data is the absolute worst possible computer problem that a user can have.

I feel for anyone who had this issue over the past 3 months. Almost every single situation ended up with an erase and reinstall losing all data. You can talk all day about how users need to backup files. We all know that in a real world situations this is not always done.

The good news is that we have now a solution to fix this issue for anyone who is currently having this issue or will in the future until Apple fixes this problem.

I will update as soon as I have more information.

16. If you are seeing this issue, please let Apple know.

I’ve filed an Apple Enterprise Support ticket on this issue.

Please file a FeedBack Report, call AppleCare or file an Apple Enterprise Support Ticket.

This will help Apple Prioritize the issue and get the issue resolved ASAP!

17. Credits.

Hat Tip goes to @stevemaser for pointing out the space issues with the big sur upgrader and @crsleeth for getting me to look deeper into this issue.

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255 thoughts on “Big Sur Upgrade not Enough Free Space = Serious Issue & Possible Data Loss! UPDATED”

  1. I can confirm that one of our users used the 16.7.02 Installer to upgrade their Mojave to Big Sur (11.5.1) and faced the same boot loop issue ending up in a complete loss of their files, apps and settings, booting up to a clean version of Big Sur. They possibly had less than 35.5GB free on their hard drive when they attempted to upgrade (our reports from the previous day showed 19GB free), but no “low space” notifications/warnings appeared for the user during the process. No FV2 encryption enabled.

  2. This didn’t work for me unfortunately. I had this issue (Big Sue won’t install with less than a minute remaining) so I followed the instructions and installed Mac OS on an external drive and booted from there. I checked my Mac drive and it has 438GB space so space is clearly not the problem. There must be another issue so I will now have to erase my drive and reinstall Mac OS.

  3. I cabled between my 2013 MBPro and my new one, put old one in target disk mode, entered in my PW when the dialog box popped up, I can see my HD on my old computer but NOT the files. It appears to be completely empty. When I look at statistics on the HD it shows it’s full. What do I need to do to actually see my files on the HD? Thanks.

    1. Jim, open up disk utility and then look on the left hand side. You should see under Target Disk Mode Macintosh HD and Macintosh HD – Data
      Right click on Macintosh HD – Dat and select mount, all your files should be there.

  4. I just wanted to say thank you. I followed your instructions and the problem was solved. The apple care people couldn’t solve it and I was going to lose a lot of data. I really appreciate all the time and energy you took to explain this issue and help solve the problem.

  5. I just had a client run into a free space issue with the 11.4 update. (on an M1 Mac mini, 16 GB ram, 512 GB storage)

    I’m not sure if 11.4 doesn’t check for free space, or it just didn’t require enough space to do the update.
    When I was called, the computer wasn’t booting, it would only go into the recovery setup, we were able to check from there, and it was reporting only 18.1 MB of free space. The user did not know how much disk space there was before it started the OS update.

    I tried to access the drive contents by sharing the drive – connected with Thunderbolt 3 cable, it could see the computer, but would get an error about it being “not found” when double-clicking on the drive (tried multiple ways starting with Guest access). This is something I was immediately concerned about when I read about the change from Target Disk Mode to the SMB Sharing, if there is a problem, the disk may not be able to be shared.
    Using terminal in the recovery boot I was able to find some things that could be deleted that I know amounted to many GB of data. But the free space was not updating.

    So finally I had to go through the process on another Mac mini of doing an Big Sur install onto an external USB drive. Once that was setup, I could finally boot the problem M1 Mac mini from the USB Drive and access the drive contents, at that point the free space finally updated. I was able to then go through their drive to look for any other data that wasn’t needed to free up even more space.
    After that I could reboot back to the recovery, and do the macOS re-install – it then came back up running with all of the user data, etc. all working properly. So at least the new way it splits OS & Data partitions did what it was supposed to.

    Once this all seemed to be fixed up, the SMB sharing on the drive now worked. So I’m not sure what prevented it from working – but maybe was related to the low disk space, or that it didn’t shut down correctly (crashed during the update)

  6. All I can say is a huge Thank You, Mr. Macintosh! I am literally spent after spending the last day and a half doing remote IT with my daughter, who lives 1500 miles away. The Big Sur upgrade (which I have abbreviated to BS…pun intended!) was required by the online exam platform she is required to use and had to be done this week. Long story short, only with the help of your article were we able to unlock her encrypted data, finish the BS install, and get her MacBook air up and running again perfectly.

    Before upgrading I had her check all of the Upgrade requirements, and her MBA met them all, including having enough storage to do the upgrade, but only just at 49GB. The Apple website only mentioned needing 35.5, so I figured she was golden. The upgrade seemed to go okay, but then we ended up in the “Error Occurred” loop mentioned in your article.

    I spent hours researching on Apple Support Community and Discussions. Their only “solution” was to restart the computer, which, of course did not work. In the morning, I googled again and came across your article. The description of the issue as well as the pics you posted were super helpful. I could see we had the exact problem with the exact error message. The clean way you wrote the article made it easy to read and encouraged me that all was not lost. Both videos were extremely well, done…yes I watched the first video in its entirety, several parts more than once.

    Not knowing if her HD was encrypted or not, we tried the Terminal method first. We could only get so far as the HD-Data did not appear. Then my daughter found a friend with not only an extra MacBook, but running Mojave as well! Our biggest issue was finding a Thunderbolt2 cable to connect the two when in target disk mode. Thank you to the Best Buy guy who referred her to an obscure little computer store down the street where they had the cable.

    Not everything went to plan, the older cable was a little slow, only the Update disk and the Macintosh HD-Data disk appeared on the host, there were no dmg files that we could find. Aside from all that, we were able to delete a bunch of junk and recoup 50+GB of space, which allowed the BS upgrade to finish once we restarted her computer.

    I know this is long, but I want to encourage anyone else with this issue: do not freak out, all is not lost. If I can walk my IT challenged daughter through this via the telephone with ultimate success…no data lost, you can do it too…but only with the help of Mr. Macintosh! Thank you Again!

  7. Hi. I have an older MBPro 2013 and ran into this problem, my HD was encrypted. I had a newer laptop laying around but no cable to connect them as target drives and a bootable drive wasn’t working. If anyone else finds themselves in a similar situation this is what I did to get Big Sur back on track…

    I was able to get into the terminal from recovery mode (restart CMD+R). Once there, using info on the below page, I was able to unlock the Macintosh HD – Data drive and manually delete items using the terminal command:

    https://derflounder.wordpress.com/2019/01/15/unlock-or-decrypt-your-filevault-encrypted-boot-drive-from-the-command-line-on-macos-mojave/

    The relevant commands for terminal were:

    Get a list of the hard drives by their volume names (all code entered without quotes):
    “diskutil apfs list”

    Then unlike the drive by it’s volume name:
    “diskutil apfs unlockVolume /dev/disk1s1” (your drive will be numbered differently and you will need your user password to make that happen)

    From there it is just a matter of moving around the drive drive and deleting what you can. For a cheatsheet on terminal commands, go here:

    https://www.makeuseof.com/tag/mac-terminal-commands-cheat-sheet/

    One thing that was a pain…in recovery mode the “du” command was not available to me so it was a bit of a guessing game when I got to where I needed to be – but I generally knew where the big files were typically and using “ls -lh” gave me a file listing view within folders of file sizes so I was able to delete the larger files.

    I ended up deleting a bunch of Apps that I knew I could just re-download, emptying the downloads folder, dumping Photos that I knew I had backed up.

    BTW…iPhoto images are located here within a deep folder structure in case you are looking for them:
    iPhoto 10 picture library:
    ~/Pictures/iPhoto Library.photolibrary/Masters/

    iPhoto 9 pictures location:
    /Pictures/iPhoto Library/Masters/

    iPhoto 8 and prior versions pictures location:
    /Pictures/iPhoto Library/Originals/

    I hope this helps someone.

  8. Hi,

    Back in March I tried upgrading my OS to Big Sur from High Sierra. I ran into an issue where I had enough room for the installer to install and then initiate the Big Sur installation but then was stuck in a boot loop. After some investigation and help from a Mr. Macintosh video, I was able to discover that the installer did not give a pop-up indicating not enough storage was available for the entire OS installation, only enough was available for the installer. See the article here for more information:

    https://mrmacintosh.com/big-sur-upgrade-not-enough-hd-space-serious-issue-possible-data-loss/

    I borrowed a friend’s MacBook with High Sierra and used the target disk mode to access my drives via a thunderbolt cable. I then deleted 36 GB of videos but also deleted my downloads folder which presumable contained the installer. When I tried to eject the first time I had an error. I then tried again and eventually the disk ejected. (Note I did not click force eject.) After this, I rebooted my MacBook and it was supposed to finish installing Big Sur. However, I was met with the image of a flashing folder with a question mark on it. I connected back to my friend’s computer and this is what the Disk Utility was showing: “AppleAPFSMedia uninitialized” , and “Apple SSD SM0512G Media Thunderbolt External Physical Disk • GUID Partition Map” and under that, “disk2s2 Thunderbolt External APFS Physical Store.” I also booted into recovery mode and was showing the same thing.

    Does anyone know how I can recover my data/install Big Sur without losing my data? Please help as I have years of photos and videos and never thought to back up my laptop. If you need any further information, please let me know. Thank you!

  9. A small note, but I’ve recently been poking around in recoveryOS and noticed that “macOS Update Assistant” is it’s own distinct app, separate from the “Boot Recovery Assistant” app.

    They both live within “/System/Installation/CDIS/” in recoveryOS along with most of the other recoveryOS tools.

  10. Does this fix work if you install big sur on the external hard disk and use that to boot and cut/paste or delete files from Macintosh HD – Data

  11. So my iMac is having this error, but when I mount it to my MacBook Air using High Sierra to clear up space it’s showing 708.12 GB of free space. I’m so confused on what is causing this error if it’s not a full disk?

  12. Mr Macintosh — tried doing internet recovery with my 2015 MacBook. Went to disk utility and tried going on to HD but my password prompt never appeared. How do I mount it? Please help

  13. I am still getting this error (an error occurred preparing the software update) the first time (every time) when I try to clean install macOS Big Sur in my macbook. (I use the latest installer 11.2.2) If I shutdown my device and restart, macOS Big Sur installation continues.

    I also happened to face kernel panics with previous versions of macOS Big Sur installer. Should I worry if my brand new macbook has hardware issue or something?

  14. My hero! I was one of those sad people that had not enough space, hd encrypted and bootable drives disabled and you helped me save years of work and memories!!

  15. Thanks A LOT for all the information and help/tips.

    Actually I solved it thanks to all the information above. But differently. It might be already in the comments (I didn’t read them all – 300+) . I have started in Recovery mode, then in terminal after mounting the drive I was able to delete one well known (and heavy) folder that I didn’t need to keep. Of course this is only possible with non-crypted disk which is my case. Glad I was able to avoid the data loss.

  16. Hi and thanks a lot for your work ! I used the target disk mode method and I was able to access the hard-drive of the target computer (target computer high sierra and my mac running on big sur) without having to type a password. However I could only see Macintosh HD in disk utility though, not Macintosh HD data. I did not erase nor mounted/unmounted anything but just using Macintosh HD in the finder I had access to all data and cleared enough space to reach 100gb available. I rebooted the mac pressing the option key, selected the macos installer disk, but still ended up in the same loop with the message “Storage system verify or repair failed”. I rebooted again pressing the option and this time selected Macintosh HD. The target mac booted, I could log in, a popup window opened asking to set up the installation of big sur, I did it, it a message prompted indicating that the mac had to reboot, but when rebooting I still end up on the same error message “Storage system verify or repair failed”. Tried rebooting using the macOS installer, same problem. Any advice ?

  17. I have a MacBook Air 2005 I believe. don’t have a cable to connect to another Mac. Put Mojave on an external drive and it says there’s not enough room to load it. The desktop has no icons or even a background photo. I can’t right click the data drive to show on finder. How do I delete files to make room?

  18. Hi, I am having the same issue after attempting to update to Big Sur. After much time in the phone with Apple I was able to use a thunderbolt cable and save my files onto another computer. After that occurs my computer now recognizes no drives. He starts up to a black screen. I am unable to run internet recovery mode and it tells me there are no volumes. I am okay with erasing my computer but I cannot. I was then able to run a diagnostic that says error code VDH002 that my storage device had an issue. My computer was working beautifully up until the update.

    1. I have the same issue.
      Failed Big Sur update and now my internal SSD is not recognized anymore…
      Please help!

  19. Hello Mr Macintosh,
    In your Feb 19 update video, you seem to indicate Apple has fixed the installer issue and new users will not have any problems unless they have downloaded the old installer before the Apple fix. Am I understanding this correctly?
    I just attempted to upgrade to Big Sur on the evening of Feb 23, 4 days after the video, and I currently have the screen like yours labeled “macOS Update Assistant” and “Choose Startup Disk menu – Macintosh HD is missing!”.
    I downloaded the Big Sur upgrade from the AppStore on that evening so I should have received the newest Apple Installer, correct? I do not allow my MBP (late 2017, 2.3 Core i5, 256GB SSD, High Sierra, I think FV was off) to auto-update so I shouldn’t have had an old installer. The 23rd was the first time I had even looked into upgrading my OS.
    On my first attempt at download, I did get the error message saying …..not enough free space…..need additional 6.33GB. So I went into my photos (biggest use) and deleted many. After that, I did not check new space available so I don’t know how much I cleared.
    Then I tried the process again and I was asked to allow “…?… Helper” access and it needed my admin password. I entered my password, the process started up, I thought “OK, must be working”. I left, came back a couple times and saw a progress bar and a reboot.
    Then I got the error notice and the current windows described above.
    I don’t know which installer was used but I do know I used the available download from the Appstore as of Feb 23.
    I haven’t made any attempts yet to do the TDM until I am clear on what to do. I would do this using my husband’s MacBook Air which has Catalina loaded.

  20. Hi Mr. Macintosh, first off thank you for your article. It was very helpful in troubleshooting my Big Sur start-up disk loop/no space issue. I just wanted to pass on an observation that I believe is contributing to the no space on restart issue. Mac OS 10, Mojave/Catalina, used iPhotos app to manage photos. Mac OS 11, Big Sur, uses Photos app. I noticed that the Big Sur install created an iPhoto Library Migrated Photo Library folder that preserved my 11GB of photos in iPhoto format. At the same time, the Big Sur install migrated those same photos into the new Photos app which consumed an additional 15GB. So after Big Sur upgrade, my internal HD had iPhotos equal to 11GB PLUS Photos equal to 15GB. I do not think the Big Sur space install space checker is taking photo migration into account.

  21. Thanks for your explanation so far, I’m getting stuck while trying to connect my MacBook Air 2017 to my brother’s MacBook Pro 2017 (Mojave) in the target disk mode. We only have tried using a Thunderbolt 3 cable with a USb C to USB converter to connect the laptops but nothing has been showing up. Do we need a different cable? Are there even other cable options since we have two different Thunderbolt cables? I haven’t been able to find a Thunderbolt 2 to Thunderbolt 3 cable but I’m not even sure if that’s our problem.

    Thanks so much for your help!

  22. I freed up enough space but still encountered the “An error occurred preparing the software update” message.

    – MacBook Air 2019, upgrading from Mojave
    – Didn’t have enough room, used terminal to delete files, using ‘df’ and ‘df -h’ in terminal verified I had ~55GB free. Trash was empty.
    – Big Sur install failed again with the above message.
    – Ran disk first aid on the install partition and the main Data drive, no issues

    Anyone still run into the issue even with enough space?

    I’d like to upgrade to Big Sur but am trying to not risk putting my only computer out of commission for a day again with an install attempt.

    1. Greg, try to free up some space again but this time instead of letting the upgrade finish boot to recovery. Once in click Reintall macOS Big Sur. See if that works.

    2. I was able to do MBA upgrade to Big Sur on 128GB disk and and external SSD(exfat, apfs, large file support fs).

      Disable Time Machine jobs or major file writes to your main disk
      Clean up as close as you can to 35GB free space
      Download the Big Sur DMG, 12GB
      Copy the BS.dmg ‘Install macOS Big Sur.app’ from /Applications to your external SSD volume
      Delete the DMG in /Applications (frees up 12GB space…again)
      Create an alias of the BS.DMG installer (right click dmg : alias)
      Copy that alias to /Applications where the dmg was previously (rename ‘Install macOS Big Sur’ *jic)
      Run the Installer alias from /Applications
      Tweak storage by copying/removing applications, Downloads, Language packs, Xcode?? to your external disk or another USB/DATA STORAGE media
      Installer should allow you to run on main disk now
      My MBA 2019 rebooted once to install Catalina, then needed a manual power on and a few more reboots but did load Big Sur.

  23. I’m sorry if I’m repeating anything that’s been said. I kind of pieced together my fix using this post and a handful of the comments. Just wanted to throw out there what I did as I know everyone has slightly different issues…

    I’m a TIS at a school and one of my teachers attempted to update a 13″ 2014 Macbook Air from Catalina to Big Sur using 12 gb of free space. Same problem as described, instead of stopping the install, it went on to the boot loop. Loooooong story short, I was able to boot to Recovery and *probably* could have backed up to an external drive from Disk Utility, but I chose instead to attempt to clear space using a Thunderbolt 2. (I’ve never done a full backup/reinstall before so I was hesitant) When I connected the machines, the Macintosh HD and the Update volumes were both visible on my desktop, but not the Macintosh HD-Data one. It wasn’t until I disconnected in frustration that I saw all three volumes yelled at me for disconnecting improperly.

    Ultimately, I found the Data drive using Disk Utility, right-clicked to ‘open in finder’ and there it was! Cleared like 35gb of space onto an external drive, completed the install, added the files back and we’re good to go! This was after three separate Apple techs told me it was a lost cause and after each started the solution with ‘well Apple always says to back things up before you do an update’, maybe the worst, most out of touch line in all of customer service, particularly during this Apple screwup, particularly towards a teacher in 2021…

    Anyway, I can’t thank you enough for this. It was quite the relief to find this post, to say the least.

  24. Hi Mr. Macintosh
    First of all, thank you so much for your solution to this problem! I was able to recover all the data on my girlfriends MacBook.
    While accessing the MacBook in Target Disk Mode I realized that some of the data was corrupted, and that I wasn’t able to back up all of it.
    The solution to this problem I found, was to create a disk image of the MacBook and opening that image on another Mac with Mohave installed on it. This way I was able to enter the password, unlock Macintosh Data and recover all the data on it.
    Hope this helps if somebody is in the same situation as me and has to make sure she/he is able to back up absolutely every single file.

  25. I’m having MacBook Air 2018 as a target Mac (encrypted) and MacBook Air 2017 as a host both running Catalina. I did everything what you did in the video, deleted Macintosh-HD in target disk mode and got into my data. What was weird, before I deleted Macintosh HD, it seemed empty in Finder. I also had Update- disk in disk utility. I deleted files, so I had 45 GB free space. Then I restarted my target Mac, but it still fails the Big Sur update. Disk utility shows now Macintosh HD, Macintosh HD- Data, Macintosh HD-Data-Data and Update. Macintosh HD is using 848 kt and Macintosh HD- Data is using 33 kt. Also I can’t mount the Macintosh HD-Data-Data, I think my data is there. Should I erase both Macintosh HD and Macintosh HD-Data and try to delete more files to have more free space? I’m not sure what the problem is. Any ideas?

    1. When Big Sur is reinstalled a new volume group is created. In this case since Macintosh HD – Data was there, it created a new one called Macintosh HD – Data – Data. You can go back to recovery and verify this by clicking on “Macintosh HD – Data” and looking at how much HD Space is used. Macintosh HD – Data – Data should only have about 2.5GB used. OR it could actually be your real data drive. You need to check for sure before you erase anything!

      1. Macintosh Hd: 897 kb
        Macintosh HD- Data: 49 kb
        I can’t mount Macintosh HD-Data- Data. In disk mode I can also see macOS Base system which takes 1,58 GB, this is under ”disk images”.

  26. Hi Mr Macintosh.

    I have connected my 2014 MBP (failed while updating to Big Sur from Catalina) with my 2019 MBP through thunderbelt. I can found the Macintosh HD is mounted and but not the Macintosh HD – Data. After I erased Macintosh HD, however I don’t see the pop up asking for password when I try to mount HD – Data, instead I still see a pop up saying “The disk can’t be unlocked. A problem was detected with the disk that prevents it from being unlocked.” Should I find a MBP that runs Mojave or Catalina as the 2nd laptop for TDM?

    Another issue I found is that only when I reboot my 2019 MBP can I find external drivers from my old MBP connected through thunderbelt. I wonder if it is a normal case.

    Please help me on this! Thanks a lot!

    1. Once you erase Macintosh HD, you will need to click on Macintosh HD – Data and then select the Mount Button. Then you should get a prompt for a password. You can also try right clicking on Macintosh HD – Data and select Show In Finder.

  27. This article is so helpful! Although I am a bit confused. I have a 2014 Macbook air. It is my only mac so I am going to try the external disk approach. However, I havent used my computer in a long time so the latest update I had before trying to update to BigSur was MacOS Snow Leopard. Is it the same process? Do I have to download a different one to the external drive other than mojave?

    1. Hmm, double check as Snow Leopard can’t be installed on your Mac. For the external hard drive You can install anything 10.13 or newer and it will work for unlocking your internal hard drive.

  28. hi,

    when i try to boot from USB macOS Mojave, after it loads the bar, I get Ø on the middle of the screen and I’m stuck here. The disk is encrypted. anyone could help ??

      1. MacBook Pro ( Retina, 13-inch, Early 2015)
        i5 processor – 2.7 GHz Dual-Core
        8gb Ram
        120 Flash Storage

        I have 2 x MacBook Pro. The first one wasn’t encrypted – worked to finish the install and the updates of BigSur
        The second one is encrypted and get the No data error when I try to boot Mojave, also I tryed to boot High Sierra and got the same error.

        1. @Mr. Macintosh, do you have any resolution for me please? I still have one laptop blocked :(.
          Thanks in advance!

  29. Getting following error while trying to access the folders
    “mydocuments” can’t be opened because the original item can’t be found.”

  30. Hi,
    My sister-in-law run into this issue with a 2013 MacBook Air with 128GB SSD and as far as I know she did not use Filevault or have a Time Machine BU despite my pleadings when she originally got the computer to BU. After searching I found your very helpful post. I have MacBook Pro running Mojave so I bought a Thunderbolt 2 cable and connect ted MBAir to the MBPro in Target mode. Disk Utility shows the following Macintosh HD – Data, Macintosh HD Data – Data, Recovery, Reboot, and VM. There is no Macintosh HD. All of the items can be mounted except the Macintosh HD – Data – Data. The Macintosh HD – Data has a System folder inside with all the assorted System folders like Applications etc. The Macintosh HD – Data -Data stays grayed out regardless the number of attempts to mount. I copied the contents of the Macintosh HD – Data to an external and the total amount was 11.9GB with is consistent with a system folder. All the other mounted volumes do not make up anything near 120 GB. Any suggestions? Is the Macintosh HD – Data has any hidden User Data folder? I am at a loss. I will be grateful for any help, suggestions.

    1. This is a common mistake when reinstalling macOS. If the person reinstalling macOS does not erase the entire volume group, duplicates will be created.
      “Macintosh HD – Data, Macintosh HD Data – Data”
      This should be the layout

      Macintosh HD – Data = System Folder
      Macintosh HD Data – Data = The user Data folder.

      When you try to mount “Macintosh HD Data – Data” what happens? Try right clicking on it and select “show in finder”

      1. After clicking Mount Data – Data never shows up on the Desktop, and right clicking Show in Finder is grayed out.

  31. thanks alot for this web! finally i can save my data, delete some files, so i can continue update big sur. i have macbook air 2017. first i used macbook pro 2012 with high sierra as 2nd mac using thunderbolt 2 to thunderbolt 2 cable but it can’t detect my macintosh disk. i tried again with macbook air 2013 with mojave and it works! it can detect my macintosh disk. i delete some file until i got free storage about 30 GB, eject disk, turn off my mac, turn on again, and violla!

  32. Hi,

    Thank you so much !!

    I applied your last update (19/02) and got back all my datas and finished the update of Big Sur.

    – Host : MacBook Air M1 – Big Sur
    – Target Disk Mode : MacBook Pro late 2013 – High Sierra

    Cables : I used a Thunderbolt 3 adaptor to Thunderbolt 2 and a Thunderbolt 2 cable.

    All the steps were smooth following the video.

    Thanks again !

  33. Hi there, thanks so much for this article. I found it at the perfect time, just before I was going to erase my mac after two weeks of putting it off. I am in the situation of a encrypted mac, however I have access to a high sierra mac and got the relevant thunderbolt cables. so far I have been able to access my files and data (YAY!) and back them up onto a hard drive. after clearing enough space to finish the update i went to restart my mac but now after entering my log in password, i receive a black screen with a stop sign/ prohibited sign ( circle with line through it). would love any advice on how to work around this. On a side note, when looking at my drives in TDM mode, i have MAC HD, MAC HD- DATA and then also an update drive. havent seen anyone mention anything similar to an update drive. once again, thanks so much for the help so far.

  34. I have the same problem. Target mode disc (using High Sierra on working computer) only mounts Macintosh HD and Update. Disk Utility shows Macintosh HD – Data but does not mount it.
    Any advice?
    Thanks for this. I feel less lonely.

  35. Hi, im having a problem when I start up my MacBook Pro (Mid 2014) pressing and holding T key. It just appear the Thunderbolt logo, not the usb. Whats the meaning of this? I suppose that I can only access my data with a thunderbolt cable?

  36. You have saved me! I was unable to access my data in target disk mode because my computer was rejecting my password. Your update about erasing “‘Macintosh HD’ System Volume ONLY” in Disk Utility was the answer that cracked this open for me. I immediately got access to my files and was able back stuff up and clear out space. After that, Big Sur installed immediately.

    Several people at Apple told me I would have to wipe my drive, but I just KNEW that wasn’t correct. THANK YOU!

  37. Hi guys, thanks for all your posts/advice.

    I have a 2014 Macbook Air that is stuck in the loop. I tried STEP 1 and downloaded Mojave to a USB using TransMac, but I’m unable to get my Macbook Air to reboot and recognize the drive. It asks for my WiFi password (cool) but nothing else – keeps going back into the loop. How do I get it to recognize the USB????

    Any advise on how to follow through with using the external USB to reboot (at least to just get my data) would be amazing.

    Thank you!!

    Christine

    PS: genuis bar sucks

  38. Hi Mr. Macintosh
    I have a 13 inch Retina early 2015 Macbook pro running Catalina. Failed while upgrade to Big Sur and unfortunately with FileVault 2 encrypted casing this same BIG problem.

    I have another 27 inch Retina early 2015 iMac running Big Sur 11.2.1. I turn on Target Disk Mode on my macbook pro, and connect it to my iMac with thunderbolt 2 cable. I can see the Macintosh HD on the screen and a pop up window asking input user password to unlock “Macintosh HD – Data”, but it doesn’t work after I input my problem macbook pro user password.

    So what is the problem? Do I have any chance to get my data back?

    I really appreciate that if you can give me any ideas to help!

    1. For the iMac I have, do I need to downgrade to Catalina or lower version and do TDM with the problem Macbook pro to try again?
      I am looking forward to your reply for help.
      Rreally appreciated!

    2. Finally, I have solve the problem and save my data!!! Never forget to backup the files again!
      Thank you so much Mr.Macintosh

    3. I had this same problem. See my comment above. The article suggests that, while using Target Disk Mode, you use Disk Utility to erase “‘Macintosh HD’ System Volume ONLY.” Strangely, after I did that, my computer accepted my password and gave me access to “Macintosh HD – Data.”

      1. Yes! that works! I also do that to save my data, then I reinstall the macOS and now everything runs good!
        Thanks for the post!!!

  39. Apple support has failed me, haha.
    My MacBook Pro (Retina, 13-inch, Mid 2014) is stuck in the stupid install loop, although it had 20gb free prior to the update.
    I bought a Thunderbolt cable to connect the MacBook to my iMac (RETINA 5K, 27-INCH, LATE 2015). Followed all the steps to restart the MacBook in Target Disk Mode, but no matter what I do I can not access the hard drive via my iMac (running Big Sur 11.2.1). Apple support didn’t have any suggestions other than run First Aid in recovery mode and try again. If that doesn’t work, go back into Recovery mode and erase the hardrive and start over.

      1. I am having a similar issue. Tried installing Big Sur on MacBook Air mid-2013 and it is stuck on the loop. Also, bought a Thunderbolt cable to connect to MacBook to iMac (21.5-inch, Late 2012) running on macOS High Sierra 10.13.6. Restarted the MacBook in target disk mode and connected thunderbolt cable to iMac. I was prompted to enter a password for my MacBook and then nothing happened. No volumes showed up on desktop of iMac.

    1. Hi,
      I have the exactly same issue with you (my Macbook Pro is early 2015 13 inch retina, and with FileVault 2 encrypted), Is your MacBook Pro (Retina, 13-inch, Mid 2014) FileVault encrypted? Did you solve the problem now? I am really appreciate if you can give me some advice.
      Thanks

  40. Hello Mr. Macintosh,

    Thank you for your time and dedication in helping people solving this issue.
    My setting:
    • Defective Laptop: unencrypted MacBook Air 11” 2013 version on macOS Catalina with Big Sur update failed
    • Functional Laptop: MacBook Air 13” 2015 version running macOS Big Sur 11.2.1.
    • Functional Thunderbolt 2 cable
    Unfortunately I cannot see my Macintosh HD icon on the functional laptop while using Target Disk Mode.
    https://imgur.com/hJH0HZq
    https://imgur.com/a/TTf8tCx
    https://imgur.com/a/volurDv
    Do you have a solution for this issue?

    Best Regards,
    Silvio

  41. I can’t thank you enough for your article and video – I just wish I had found the video sooner. I fell in to the category of having a 2018 Macbook Air, encrypted, so my only option was to boot up in target disk mode on my husband’s mac, however he had already upgraded to Big Sur so I ran in to all the problems you referenced there. Unfortunately, I followed all the steps up, going in to disk utility and deleting Macintosh HD, but instead of erasing Macintosh HD – per the suggestion of another comment – I clicked on deleting the volume drive as opposed to erasing the whole thing. Now I don’t see any kind of reference to Macintosh HD, just the Apple SSD SM0128GB Media with a Container disk3 dropdown, and I’m not able to get anything to mount. ANY guidance you can give would be absolutely amazing.

  42. Well, something new has happened. I tried to boot into internet recovery, and for no reason I can think of, the Macbook has now started taking me into normal recovery mode without asking for my password.

    So I was hoping to try to erase the Macintosh HD partition, as some here (and elsewhere) have suggested. But I can’t see any such thing in disk utility. What I’m looking at is:

    121.33 GB APPLE SSD SD0128f MEDIA
    disk0s2
    disk1
    OS X Base System

    I have no idea what to do with any of these. And tbh, I don’t really know what a partition is, even. Just floundering about here!

    What I really hoped to do was reinstall the OS that came with the Mac (Yosemite, it turned out). But when it asks me where I want to reinstall it, there are no options – there is no image of a drive to click on.

    Would really appreciate it if anyone recognises this situation and could advise me!

    1. I now also see that if I click on disk0s2, at the bottom of the screen, it says mount point: not mounted. So if I clicked on mount, would this enable rebooting from Yosemite, maybe??

  43. Thank you so much for solving this issue. My case is the first scenario: 2017 Mac – FileVault 2 Encryption Not Enabled. After I freed up enough space following the the instructions provided, I restarted the Macbook, hoping it will automatically finish the upgrade, but there was a boot loop problem. I had to choose reinstall Big Sur in the recovery mode to get the upgrade started. Finally, I got my MacBook back. Thanks.

      1. Hi Mr Maccintosh,
        Thank you so much for sharing this to us!
        I have a question: my Macbook pro is early 2015 version facing the exactly same issue with FileVault 2 encrypted.
        So can I get my data back? Oh my god!

  44. So I Called Apple…

    (Background: I am in the situation with filevault encrypted mac). I called Apple and after 2h we went through disk utility and from there we could visualise Os X. Because mac HD disk was not there the Apple lady told me that there is no way other methods mentioned in this amazing blog w would work (target mode data nor Mojave reboot from external hard drive). Is this the case?
    I have not tried as I do not have a thunderbolt cable.
    Any help would be great…should I assume the death and loss of data or any hope left?

    BTW :
    – apparently this is not a bug from Apple point of view…it’s our fault for not backing up…
    – I have a late 2013 macbook pro and middle macbook air to perform target mode with. Will thunderbolt work here?

    1. “apparently this is not a bug from Apple point of view…it’s our fault for not backing up” – Victim blaming.
      “the Apple lady told me that there is no way other methods mentioned in this amazing blog w would work” – So the whole article is fake news?

      Sorry you had to deal with this. AppleCare has some amazing technicians, but once in a while you will have problems.

      Yes, a thunderbolt cable will work between both Macs for target disk mode.

      1. Thanks. This blog is amazing and I can only appreciate all the time that went into it. I’ll purchase a thunderbolt cable and try the target mode.
        I had a lengthy conversation on why apple does not advise to try the methods outlined by you. The answer was that these are simply not apple approved processes.
        It is a shame that instead of giving credit to the person who brought to the surface this BUG and helped so many people, the apple support takes the easy route of advising to simply erase data…

        Couple of thoughts:
        – I wonder if there are any bases to start a legal action against Apple here.
        – what do you think about the claim (from the apple lady) that if from recovery mode the machintosh HD file was not visible this means that the faulty Big Sur update cause irreversible loss of data already. They are basically telling people: data is already gone you might as well reboot and reinstall everything… thanks again

      2. My thunderbolt arrived and …another happy reader with his data safely back.
        Thanks again!

        To all: call apple and complain it is utterly unacceptable that the apple customer support takes the shorter route (for them) and advise to simply accept that data will be lost… and get your money back for your cables.
        Thanks!

  45. Hey thanks for the post, I was wondering if TDM would work with a USB-C to USB Adapter since my host computer doesn’t have any USB-C ports?

  46. Hello Mr Macintosh

    Thank you for what is, by far, the best post on the Internet to help with this truly terrible Apple problem! I am not fixed yet and think there is a new twist …. I had enough space but it STILL fails!

    I usually ask my Mac to “remind me later” on updates when they pop up so I don’t know what prompted me to look on February 15. I was then seduced by the option to upgrade to Big Sur 11.2.1 on my encrypted MacBook Pro Retina Mid-2015 running Mojave and off we went. The installer said I did not have enough space to install and so I cleared enough space (by optimising Photos to iCloud which were previously stored in full on my Mac) to start the installation. However, things then started to go wrong …

    I originally got stuck in the loop you describe at the start, with the bar progressing and a number if minutes counting down, only to run into the error right at the end. Same process on restarting the Mac. I started Googling and using Single User Mode and then things get a bit hazy. I’m not a Unix whizz (although I am a Telecommunications Consultant and have installed a lot of software in my career), so maybe I entered a command which broke things. But I managed to get into a state where the computer boots to the Mojave screen, my password is accepted, the Apple logo with an approximately 5% finished bar appears and then after 20s it reboots into this endless cycle.

    So now I cannot do anything. Furthermore, because the disk is encrypted I could not enter a password at MacOS Recovery (which is accepted at the login screen). At SUM it tells me I am running 11.2. I have some of the symptoms you describe so maybe TDM will work but I am waiting for the cables to arrive.

    In your video, you say there was a way to get TDM to work with Big Sur WITHOUT needing a Mojave Mac, but you proceed to remove the volume using a Mojave machine? Did I miss something?

    Many thanks!

    1. Yes, in that section where I am talking about the Big Sur device, I meant to run that part on the Big Sur mac not the Mojave mac. If you have a Mojave mac you are set you will be able to access your data. Heck if your 2nd mac can boot to mojave via Internet Recovery that will work! I am trying to work on an update video tonight where I will attempt with Big Sur again.

      1. Hi, I’m attempting to use TDM to save my data after Big Sur install error. The other MacBook I’m using has Big Sur installed. My password doesn’t work to access the Mac HD -Data. Can I install Mojave on the working Mac? Will that solve my problem of the password not being accepted?

        1. You bet, you can intall mojave on a 2nd partition or external hard drive and boot to it. The password will be accepted and will mount! OR if the Host Mac Supports an older version of Internet Recovery that will also work to unlock the drive! I will be going over that in my update video tonight.

          1. Awesome! Thanks for being so generous with you time and knowledge. I’m using a 2015 Macbook Air running Bug Sur as the host computer. Each time I download the Mojave installer it just disappears. It’s not in the Applications folder. So I downloaded El Capitan which saves to “Downloads”. So I’m able to create a bootable El Capitan on an external drive. Will TDM work with El Capitan? I don’t know how to download Mojave without it disappearing at completion. I’m going to try to run El Cap from the external drive and then connect the malfunctioning Macbook Pro 2018 in TDM with Thunderbolt adapter and cable. If that doesn’t work, I plan to backup the Macbook Air and Erase it. Then I should be able to reinstall the original OS for the 2015 Macbook Air (El Capitan) using Internet Recovery Mode. Then I will upgrade to Mojave. Then TDM. How does that sound?

      2. Many thanks for the reply Mr Macintosh. I look forward to the updated video.

        Any idea why I failed to install even though I passed the space check?

        Cables arrived today so I will try to fix this tomorrow and report back.

        1. So, I am FIXED, but not how I wanted to! Firstly, a huge thank you to Mr Mactintosh for the guidance here.

          As a quick reminder, I passed the space check in 11.2.1 but my installation failed. I somehow entered a loop of login page > apple logo with a bar about 5% complete > reboot. The Big Sur upgrade would not continue when I restarted.

          My cables arrived and I hooked up to my Wife’s Macbook Pro 2017 running Sierra in Target Disk Mode. Although I could see Mactintosh HD I couldn’t see the User folder. Interestingly I wasn’t asked for a password at this point but I have an encrypted disk. I decided to upgrade the working 2017 machine to Mojave (I intended High Sierra but this wasn’t available on Apple). After upgrading I WAS prompted for a password and I entered my usual one which unlocked the disk. Now I could see Macintosh HD, Macintosh HD Data and Update. So I presume this was just a MacOS mismatch whereby Sierra was too old to read my disk which was mid-upgrade from Mojave to Big Sur. I was able to access the Data disk and retrieve the one file I wanted which I hadn’t backed up. My Macintosh HD and Macintosh HD Data disks looked completely full (and both the same) by the way.

          I then intended to either clear some space or delete the Macintosh HD and reboot. However, I think I managed to unmount something important because, when I rebooted, I could no longer log in to anything! No logon screen with Mojave image in the background.
          Luckily I had already retrieved my files otherwise I would have had no idea how to remount the disk. At this point, Internet Recovery started working and I was able to access Disk Utility and Terminal for the first time. I could see only one disk with disk0s2 which was not mounted. I could not remount this disk.

          In the end I erased disk0s2 and reinstalled Yosemite as the original supplies OS and then upgraded straight to Big Sur. I have my files and a working system but it was close! If I had decided to “eject” the disk before recovering my data I would have not been able to get it back! I was being prompted to “eject” before restarting my Wife’s machine so I thought I was doing the right thing!!

          As a career Microsoft Windows user I don’t fully understand mount points, disks, partitions or drives in MacOS. I am sure this will sound like a newbie mistake when you read this but at least I got out of jail here.

          But there’s still the question of “why did I fail to upgrade when I passed the space check”.

          Many thanks again!

          Neil

          1. I have a macbook pro, I already installed Big Sur…. how do I now access those files? I don’t mind formatting my mac

  47. I am unable to enter text into the password text field. The key board and mouse work but no characters show up and allow unlock to be selected. Also can not run First Aide in disk utilities (its greyed our) and I can’t mount it because I can’t type in the password to unlock. Any ideas?

  48. I was able to delete the HD and it then accepted the password on the data HD, but it was saying i wasn’t able to access the most folders within it under one of the usernames. I updated the permissions to read + write with no luck. Thought i had found a big chunk of data i could delete (89G) but it either didn’t delete or pulled from the target disk (it was an alias folder in my corrupted computer if that matters). I restarted and ran into the same installer issue again but this time deleting the HD wouldn’t fix the encryption issue. I also have two data HD’s now. One looks like a shell that accepts my password, the other one has my data and i can’t access it anymore. I also have an “update” HD. Help! 🙁

    1. Caroline, did the upgrade finish? I address this situation at the very end of my video. Also i have a workaround for the permission issues, just create a user of the same name on the host mac then login with it. You will now have access to your files. It does sound like the update finished

  49. Mr. Machintosh thanks for helping to people.

    I have another problem that could not find any solutions far. I can not enter the password for ‘HD-Data’. Unlock button is locked and also can not write any password. Can you please help me on this?

    Thanks in advance for your all supports!

  50. Hello and thanks a lot for your incredible work!
    I have a MacBook Air 2017. It has FileVault 2 Enabled so I have installed Mojave on an external USB with 32 gb.
    When I boot to it by holding down option after reboot I can choose the external USB to boot but after that Mojave can’t be installed.
    I’m always stuck at the menu where I have to choose the drive to install Mojave after I have accepted the terms and conditions of Mojave.
    I can not select Macintosh Data and Macintosh because of not enough storage space. But I can’t choose the USB because of “read only”.

    It would be nice if anybody could help me!
    What I can do?

  51. You saved my life! I fell into the trickiest situation possible, a 2018-2020 Mac with FileVault 2 Encryption Enabled (in my case, a 2019 MacBook Air.) Recovery wasn’t accepting my password, neither did TDM, I couldn’t boot to an external drive, the system was boot-looped, the whole nine yards.

    After reading dozens of comments here, the solution that finally worked was connecting my Mac to a friend’s Mac through Target Disk Mode over USB-C and erasing the system partition (Macintosh HD). I was then able to mount the data partition (Macintosh HD – Data) with my correct password, and I was able to back up all my data, reinstall macOS through Internet Recovery, and restore it all after.

    Thank you so much for the comprehensive documentation!

  52. I finally found a solution with Filevault turned on to keep your files, where it doesn’t accept your password in terminal or in recovery mode!!
    In my case I didn’t have enough space for the installation of Big Sur to complete.
    Machine: Macbook Pro late 2013.

    What I did, was using another mac to create a bootable version of High Sierra – It’s very important that you use High Sierra because Catalina and Big sur won’t accept your password to unlock your volume, but somehow it works perfectly with High Sierra.

    So what you are gonna do, is holding your Option/Alt key when booting , and pressing Utilities in the top to open terminal. Here you can type ‘Diskutil apfs list’ to see which disc that is encrypted. In my case it was the one called Disk1s1 (you can by the command above see which partition that is encrypted)

    When you know which drive is encrypted type: ‘diskutil apfs unlockvolume disk1s1’
    Your mac finally accept the password that it wasn’t recognizing before, and your drive is now unlocked.
    Now delete files in the terminal.
    To make it easier for myself and not having to delete files within the terminal, i made a disc partition on the bootable drive, of at least 20 GB to install high sierra and in that access my now decrypted harddrive. Make the scheme GUID and EXTENDED Journaled.

    Now delete files so you have at least 46,01 GB of free space to install big sur.

    To summarize:

    1. Create a bootable version of High Sierra
    2. Hold your Option/Alt key when booting with the usb bootable plugged in
    3. Click on Utilities in the top, and click on Terminal.
    4. Type ‘Diskutil apfs list’ and find the encrypted drive.
    5. Type ‘diskutil apfs unlockvolume diskXXX’´and enter your password. (In my case it was disk1s1)
    6. Start deleting files in terminal to clear at least 46,1 GB of free space to fulfill the installation.

    Extra step:
    7. If you don’t want to delete files in the terminal, make a partition or plug in another harddrive of at least 20 GB where you can install High Sierra and access your Macintosh data drive.
    Open the folder Users and start deleting.

    Hope this helps, as I really struggled and used several hours because of this bug.
    Let me know if I can help you in any way.

  53. Thank you so much for sharing your thorough investigation on this issue! My MacBook is a 2013-2017 Mac with FileVault 2 Encryption Enabled, and the 2nd Mac I have is running Catalina, so I am excited to hear if you have an idea of when you expect your fix instructions for this is coming? Thank you so much in advance.

  54. Hello,

    I’ve encountered the problem and struggled a lot, including clearing NVRAM and SMC. Nothing would solve the problem. Command + R, Shift + Option + Command + R etc.

    Shift + Option + Command + R can get me through disk utilities, however there is nothing in /Volumes other than an ‘OS – X Basic System’. No Macintosh HD, or Macintosh HD – Data

    It’s weird that there is no Macintosh HD for me, only Macintosh HD – Data, and Macintosh HD – Data – Data

    So far, no way I was able to mount the Macintosh HD – Data – Data (also not sure why there was two data, because there is another portion that says Macintosh HD – Data – APFS System Volume)

    Other recovery mode leads to enter a pwd that the system will not accept.

    It seems by clearing NVRAM and SMC will make things worse.

    Any suggestions?

    1. I was in the exact same situation as you, down to having the volumes named the same, unusual names. What worked for me was erasing the system partition through Disk Utility (Macintosh HD – Data in our case). Once you’ve done this, Disk Utility will finally accept your password and you should be able to mount your data partition (Macintosh HD – Data – Data in our case).

      Your system will now be unable to boot into macOS (because we just deleted the system partition), but all your personal data and apps will be recoverable since you can now mount the data partition. From there, all you need to do is copy the data to a backup, reinstall macOS, and copy the data back.

      1. Hello May! Do you mean that you erased the partition called OS X Basic System? If so, what did you do afterwards?

        Thanks!

  55. This is a highly informative post. It is my only chance to save all my PhD work on my Mac. I have a 2015 MacBook Air, and the issue I am having right now is that my own Mac shows Thunderbolt icon only (no USB), which I think means that I will need to connect my Mac to my friend’s via thunderbolt. I am having a hard time finding a thunderbolt 2 to thunderbolt 3 or USB – C cable. I can’t even find adapters! Do you have any suggestions?

    PS. My Mac falls under the Encyripted 2015 MacBook Air (no T2) & I have a Macbook Pro 2019 with High Sierra to use as a host device to rescue my data

    1. Yes, as soon as you can get that cable you should be able to access your data on the Host Mac. A Thunderbolt 2 cable with a Thunderbolt 2 to Thunderbolt 3 dongle will work great.

    2. Coskun,

      I have same problem, too. also I have a password problem that I can not enter any.. I am doubtful that even if I try TDM mode, ı most probably not able to unlock the disk but. Where do you live? Maybe we can share the cost of cable as they are too expensive in Turkey?

    3. Coskun, i have almost same problem. Where do you live? Maybe we can share the cost of thunderbolt cables which are really expensive.

      1. Merhaba Engin,

        Unfortunately, I am currently in the USA. I did end up buying both Thunderbolt 2 cable and the Thunderbolt 3 to Thunderbolt 2 adapter I needed. & I was able to solve the issue by following the instructions provided in the video. I have everything back and my MacBook is running as if nothing happened. Special thanks to MrMacintosh!

        1. Hi Coskun,

          I am happy to hear that you solved the problem. I hope that I can find a solution as well to mine.

  56. Hi,

    many many thanks, your analysis in the video solved my problem.
    1 big-sur-update-victim 2015 rMBP15″ 10.15.7 with filevault, 1 catalina 10.15.7 mb-air 2012, 1 Thunderbolt cable
    Differences to your video:
    – Two partitions, 1 update, 1 macintosh hd – data. Data with still something like 12 GB free
    – Big-Sur update failed when the progress bar showed something like “less than 1 minute remaining” for many minutes
    – Mounting the data partition with disk util simply worked (asked for password, which actually worked).
    I then followed the steps to just delete some data that I will later restore from a USB Time-Machine drive and rebooted to let the big-sur installer finish its job.

  57. Hi,
    I met the same problem on my 2014 mac book pro. My mac book pro does not have USB-C and Thunderbolt 3 port. I use Thunderbolt to Thunderbolt cable to connect to another mac, I can boost from the external mac but immediately my problem mac was ejected, is this because of the cable? My problem mac does not have USB-C and Thunderbolt 3 port, how can I fix this issue?
    I also tired to boost from external hard drive, I could not delete any files from the boosted OS.

  58. Same issue here and brought my laptop to the Genius Bar and a professional data recovery company, and both couldn’t fix the issue. After stumbling on your article and attempting to try your solution, I suddenly can’t find “Macintosh HD” “Macintosh HD – Data” in my Disk Utility anymore. This is all I can see on my screen: https://imgur.com/gallery/C8hogcp
    Any idea what happened?

    Please help! ☹️

  59. You sir deserve a statue !!!

    was able to get the important files to safety.
    I can not thank you enough !!!

    grtz

  60. Thank you very much for the thorough video. Thanks to this post, I was able to recover my data (which was my most important goal – thank you very much again), but now I have the duplicated Macintosh HD – Data on Disk Utility. Since I have used the Mojave option, I did not empty the Macintosh HD disk, and therefore I am afraid of erasing it. Does this duplicity have any implications? Does it pose any danger?
    Is there any way of fixing this duplicity without losing any of the data? I watched the final part of the video, but the information on my screen is slightly different…
    I would be very grateful for any hint. Thank you again for the incredible post and video!

  61. Hi, I had the issue where a macbook pro 2016 with an encrypted 2tb hard drive got hung up in updating from catalina to big sur. It kept booting into the big sur installation, but it was not able to complete the installation. I figured out that it was because I did not have enough space on my hard drive. I cleared the nvram and my mac no longer booted into the installation, but into a catalina login screen, but when I logged in, the system did not load (bar went to about 10%). When I tried to boot into recovery mode (command r), my password was not recognized.
    Following the advice of this forum and others, I realized that there is something that happens to the recognition of your password during the installation. When I tried to boot my mac in target disk mode and tried to hook it up to a macbook that ran either the big sur OS or the catalina OS, it prompted me for a password, since the drive was encrypted, and the password was not recognized.
    However, when I hooked my mac in target disc mode to a macbook that ran high sierra, my password was recognized, and I could transfer my files for backup. I deleted enough files so that the big sur update could resume, but it did not, and I was stuck in this loop of booting into the catalina login screen, the progress going to about 10%, then screen dark, apple logo, progress to about 10%, and then back into the catalina login screen.
    Then, by reading a bunch of forums, I ran the verbose mode during startup, and found the following error in the writing “failed to unwrap meta crypto state,” which led me to wonder what happened if I decrypted my drive using the external bootable usb with the high sierra os.
    It took 3-4 days for my drive to be decrypted.
    However, today, the drive decryption was completed, and I booted into recovery mode, which now enabled me to reinstall big sur os.
    I did so, and the installation took place successfully.
    All of my files are intact, and it is as if my installation occurred as originally planned, with the exception of a few files that I removed (backed up) in order to have enough hard drive space to effectively perform the big sur update.
    Hope this helps!

    1. This is the same problem for me. Going to setup a high sierra os bootable usb now. See if I can decrypt my drive. 🙁

      1. It took 2 days for me to decrypt my drive and the in recovery mode I could restart the installation of Big Sur.

        So big thanks to you Aleks Kalnins for sharing your solution!

  62. This is incredibly thorough, thank you!

    I have an encrypted Mac (a 2014 Air, running Catalina – no idea why I activated the vault) so need to use the usb option. Forgive me if I am missing something obvious – how do I get Mojave onto the usb without my Mac?

    Thanks for all your effort and help with this horrible issue.

    1. No problem Tom, this is a complicated issue for sure. For your situation, just to be sure when you enter recovery you are prompted for your password that does not work right?

        1. (Getting access to another Mac would be tricky, which is why I’m interested in the Mohave / usb approach)

          1. Hi, this is the approach I used.
            I’m able to boot to Big Sur on a flash drive. Was able to access my Macintosh HD-Data. Thanks you Mr. Macintosh. I can see my data etc and started to delete the files I do not require (remembering to clear the trash bin). However, now that those files are gone, the storage space has not changed. What can I do to truely delete this files? Again the trash can is empty.

            1. I did just the same thing, but the storage space didn’t change on my computer either. What should we do?

      1. I followed your guidance from YouTube video, deleted almost all users files on terminal but I still don’t have enough free space. My systems shows that I have only 13GB free! Where does the rest 107GB hides, what else should I delete to free the additional 20Gb. I don’t have any videos or large files in my MacBook! Thank you in advance for your support.

  63. Hi, I just wanted to say a VERY BIG THANK YOU MrMacintosh guy, you single-handedly helped me fix this ridiculous issue caused by the not-so-genius Apple!
    I have a 2015 Macbook Pro with only a 128GB SSD and was running Catalina before attempting the Big Sur update. The update notification said I only need 12GB for the update and I think I had around 22GB free at the time so I went ahead and clicked install… BIG mistake! I was stuck in the endless loop and from Googling on my phone I found out from on website that it was most likely due to lack of free space. I watched your video and around the 30 mins mark I followed the steps of removing files via Terminal in recovery mode (accessed via rebooting and holding down CMD+R key for those wondering) since I did not have access to any other computer or Mac and I felt this was the best option for me. Before I began I did a quick check in disk utility and it said I only had 11GB of free space, which was worrying because as I said prior to downloading the Big Sur update I had around 22GB and I knew I didn’t have many single big files I could easily delete like your .dmg examples.
    Terminal is a bit tricky and relatively new to me, so thank you so much for a very clear and beginner-friendly explanation on how to navigate through it. However, I had no idea how to see the sizes of particular files/folders despite trying to look for help on Google with commands like (du -sh*) which did not work at all so I was really unsure how big any of the files that I was deleting actually were. I was also trying to delete just one or two of movies I had, but in Terminal it’s way too easy to make mistakes and I accidentally deleted my entire Movie folder! After removing some more unnecessary files that I had in my Downloads folder (which I was blindly hoping were big files) I went back to Disk Utility to see that I now had 28GB of free space. This was an okay improvement on the 11GB which it said I had but was worryingly close to the 22GB which I started with before the update. I couldn’t think of what else I could delete without removing Apps which I had no idea how to do in Terminal, so I just crossed my fingers and clicked “Reinstall MacOS Big Sur” in the Recovery Mode screen, and let it do its thing for about an hour. To my suprise the 28GB was enough and it worked! After setting up Big Sur I went in and saw that I now have 43GB of free space..Bizzare!? Anyway, I just wanted to share my experience and thank you so much for everything MrMac it’s really very appreciated, Thank you for doing God’s work! 🙂

    1. You bet Grogu! At the end, the big sur upgrader files are removed from the root of your drive. The folder was called “macOS Install Data” and was about 13GB, so that matches right up to your 43GB after the upgrade was complete. I should have gone into more detail in the terminal section as like you said it could be intimidating and easy to make mistakes. I’m just glad that you were able to save your data and get macOS Big Sur installed! We should all get “Achievement Unlocked” awards! haha 🙂

    2. Hi. Could you please help me? We have the same problem and i dont know what to do ): thanks a lot

  64. Thanks for the YouTube video you upload regarding this issue. I currently have an encrypted Mac but don’t have access to another. In the video you mentioned the only way is to use TDM to another in order to save your data. Is it still possible to boot it to a Big Sur iOS installed on a USB stick, delete the Macintosh HD (not the volume group) in order to access the Macintosh HD-Data to delete files? Similar to what you did using a Big Sur Mac on your YouTube video around the 50 minute mark.

    Thanks.

    1. Paul, the problem is if you are encrypted you are locked out of recovery. When you enter recovery you are asked to enter in your password and it does not work right?

    2. My experience is that if you boot into Single user mode you can get to your encrypted data partition. I was also not able to get to the Data volume using Recovery mode.

  65. Thank you for investigating and solving this issue!!! I have a mid 2014 MacBook Pro and I ran into this issue trying to upgrade from Catalina to big Sur. I spent ages talking to Apple support and they told me there was nothing I could do except delete all my data (not an option) and the Apple ‘Genius’ people told me the same thing. They knew of the issue and said only one person had ever solved it and saved their data. Thankfully I took my laptop home and found this article!!!

  66. I am experiencing this issue however my mouse is not operating now either. I believe I am in the following category – 2018-2020 Mac – FileVault 2 Encryption Enabled
    I don’t currently have access to another Mac
    How do I release the mouse to even start to attempt to resolve the issue?

  67. I haven’t been able to get a 2nd machine with correct OS or cables yet.. my problem is minimac2018 with FileVault ( I think )- so am seeing if I can find a way to download Mojave to external drive – can anyone share how to do this? And will it erase my data? Although I’m not sure if my data is already gone – I finally managed to get to Terminal and it isn’t showing the Macintosh HD – Data folder ; only MacHD & macOS Base System. Does that mean I’ve lost everything already?! Oops 🙁

    1. Don’t worry, your data is most probably not gone. If you manage to get to a terminal using Recovery or Single user mode then the data partition might not be mounted yet. I posted earlier on how to mount the data volume in Single User mode (Ctrl – S). Via this you should be able to get to a point where you can find your Data volume and mount it. Do you have any external storage to mount so you can copy data from this volume if you need to move data?

  68. Here is a solution to this issue that doesn’t require any additional hardware, USB sticks or cables. But you have to be comfortable with a root shell. !! WARNING !! You can do serious damage in a root shell. Please be careful and use this at your own risk. A root shell is as effective as a loaded gun, it will quickly, happily and permanently delete your entire system with one 2 letter command plus flags in the wrong folder.

    I ran into this a few hours ago while upgrading an old MacBook Air with little drive space left. I believe I would fall under case 2) “2013-2017 Mac – FileVault 2 Encryption Enabled” above.

    Being an avid Linux/Unix user I resorted to fix this via the Single User mode boot option (root shell). To get in to Single User mode, reboot your mac and hold down the Command and S keys (Cmd-S).

    The solution here is to 1) Find the macOS Data partition, 2) Mount this partition to a folder, and 3) Delete enough data to unblock macOS install.

    1) At the # prompt, I re-mounted my root partition in writable mode. This might not be needed, but I needed a new folder as mount point.
    # mount -uw /

    2) I created a new folder “jtest”, this was my mount point for the volume in the steps below.
    # mkdir /jtest/

    3) Now I needed to find the data volume. Diskutil doesn’t work here, very nice, not! So I resorted to list all disk devices.
    # ls /dev/disk*

    This will give you variations like this, where each line represent a disk partition/volume

    /dev/disk1s1

    4) I tried mounting paritions one by one until I found my data parition:
    # mount -t apfs /dev/disk1s1 /jtest/

    If the partition is not the one you are looking for, unmount it like this:
    # umount /jtest/

    To see what you have mounted currently, simply run:
    # mount

    Continue until you see the mount command spit out something like:
    “mounted volume: Macintosh HD – Data”

    5) Now we have the Data partition mounted and available, now delete data to allow install to proceed

    If you find and mount the “Macintosh HD – Data” partition, your user [username] data will now be available here:
    /jtest/Users/[username]/

    I used rm with the infamous recursive and force flags to clear space. Remember you are root and can delete anything and everything at once, especially with the mentioned recursive and force flags. Please make sure your in the right folder/location with pwd which prints the current folder location
    # pwd

    To see how much data is available, run this:
    # df -h

    Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
    /dev/disk1s1 xxx xxx 123GB xxx xxx xxx xxx /jtest

    6) Cleanup and reboot

    !! Warning !! In the commands below, please delete jtest with rmdir and not rm. If the data volume is not properly unmounted, then rm with force and recursive flags on /jtest/ WILL DELETE ALL YOUR DATA mounted in the jtest folder which is probably not what you want. By using rmdir we are ensuring that we only delete the empty unmounted folder, rmdir will not delete a non empty folder.

    # umount /jtest/
    # rmdir /jtest/

    And finally, reboot
    # exit

    1. This approach worked on deleting the files, but still can not detect the Macintosh HD in recovery mode.

      1. I am glad you were able to mount the Data drive and clear enough data, but regarding your second part of the sentence. I was also not able to mount or find, or log on during Recovery mode. In fact Recovery mode was completely useless to me. Single user mode let me mount the data partition and clear enough space. After that I rebooted and the installer looped again but this time it could finish.

        I do not know if this differs from what you experience. Does the Bug Sur installer not keep going after your delete enough space?

    2. I’ve not tried, but maybe if the system level instruction set is still fine, maybe we can plug in a hard drive, format it, mount both drives of Macintosh HD and /dev/$your_mac_disk$, and copy the files over?

      1. Yes I definitely think you can do that. The main problem here is that very few system services will be running in Single user mode. Sadly a lot of the MacOS services available here require additional frameworks to be loaded, for example disk util is not available in single user mode.

        To mount a drive, USB or otherwise will require some digging in finding the PCI/USB bus ID under the /dev/ folder to mount, but when mounted you should be able to copy data over to, in order to clear enough space for the installer to continue.

  69. Thanks for the article. I was trying to create a bootable USB on Windows but it wouldn’t show up in the Startup Manager. However, there were two options there: Update and HD (not sure the exact names now). I started from HD and loaded my Catalina. I was able to delete Big Sur Installer so it loads fine now. However, I now have a drive called Update on my desktop. It seems to be the same size as HD but I can’t remove it. Every time I eject it, it shows up again after the restart. The biggest files there are .im4m. Not sure if I can just delete it.

  70. Hi, I managed to resolve the issue differently and wanted to share.

    Boot in recovery mode holding down CMD+r at boot
    from the menu find the ‘terminal’
    using the terminal find your home directory, then delete all the files you don’t need to clear some space (find large files using a command similar to this “find . -type f -size +4096c”), delete them.
    restart your mac, done!

  71. What do you recommend for a MacBook with only Thunderbolt 2 and the computer I am transferring to has a Thunderbolt 3 connection. I look at cables online and a lot say they’re not recommended for a Thunderbolt 2.

    I think I was running Catalina, not sure what the other computer has for an iOS.

    Thanks for helping!

  72. Hello

    It’s actually POSSIBLE to access Mac with T2 chip in Big Sur (not sure about Catalina)!

    My failed Mac is a Mac mini 2018 with T2 chip and had enabled FileValue

    I plug Mac mini’s TDM with MacBook Pro 2019 that runs Big Sur, and when I enter password it did failed, however, after I tried enter 3 times password and the prompt windows close itself, I open disk utility and then find out I AM ABLE TO open Macintosh HD – Data in finder!!!
    Cool, at this moment I decided to give back upgrades and return the Catalina, so I deleted Big Sur installer in Application folder as well as the big folder in the root of Macintosh HD – Data called something like Big Sur upgrade data. But then the problem comes, when I reboot the Mac it shows circle with a line through it. I restart, enter recovery mode by press cmd+r, the Mac mini still cannot find any system volume; then I restart again, this time press option when start up, the volume appear in screen is call MacOS installer instead of Macintosh. So I am current stuck in this step.
    Now I can still enter TDM and read Macintosh HD – DATA in Big Sur MacBook, everything in root directory is same as my functional MacBook.
    Please help me on change original volume bootable, Thank you

    1. Hello Yuyang, you were so close. In testing I realized the same thing! After entering in the password 2-3 times Macintosh HD could mount and I could mount Macintosh HD – Data with Show in finder.
      Your problem is that you deleted the macOS Install Data folder. The Big Sur Upgraded needed this information to finish the upgrade. You are now left with a good data volume but an erased Macintosh HD System Volume. Before you continue make sure any critical information is backed up first. In recovery you still should be able to still see your drive, you will need to unlock it with disk utility the same way you did in TDM. Then you can reinstall Catalina on “Macintosh HD”

  73. Hi.
    We are having the same issues but cannot access with a second Mac (which is on Mojave, Files are encrypted).
    We have tried to connect the troubled Mac via USB cable (USB A to USB C) but when we click “Target Disk” it asks for a restart…and this sends us back to the backup loop…
    Is this the wrong cable (does it have to be Thunderbolt), or what else am I missing here?

    Thank you for your help!

      1. OK that worked…but the two Macs do not connect…probably USB C to USB A doesn’t work?
        Will I have to try with a Thunderbolt 2 to USB C cable?

        1. If the target disk mode screen shows the usb logo then it should work with the right cable.

          It has the be a usb 3 A-C cable.
          Most A-C charging type cables only support usb 2.

          Thunderbolt is only possible if both macs have thunderbolt ports.

          Check the “Identify the ports on your Mac” support page.

          If the newer Mac supports thunderbolt 3 over usb-c and the older Mac has thunderbolt 1/2 using mini-dp, you need a thunderbolt cable ($29) and Apple thunderbolt 2-3 adapter ($49).

  74. Thank you so much for detailing this problem and possible fixes!

    This got me out of a jam. I needed to hunt for a thunderbolt 2 cable for my 5-year-old MacBook Air to be recognized re:target disk mode as USB did not work.

    All the best.

  75. Thank you sooo much!!! I have recovered from this upgrade to Big Sur nightmare without losing my music files that I have been working on for 3 years and spent thousands of $ on! Genius Bar and apple support were no help whatsoever!

  76. This was a huge help. My son ran into this problem when upgrading his MacBook Air and then discovered that the sync to Dropbox that he had set up had stopped sync’ing some time in 2020.

    We tried the two Mac solution with a 2020 MacBook Pro with Big Sur (by deleting the Macintosh HD and it then accepting the password for the encrypted disk). Unfortunately, while transferring all his files off, I plugged a power source to the other USB-C socket on the MacBoor Air (as it was running very low) and somehow that seemed to interrupt the connection. It then would no longer accept the password, even after allowing the upgrade to re-create the Macintosh HD etc.

    We then resorted to connecting to an 2013 iMac running High Sierra but to do that we needed to order a USB-C to Thunderbolt adapter and a Thunderbolt to Thunderbolt cable (total cost £80!)

    This then worked. Many, many thanks for all your tenacity in finding a workaround for this.

    -john

  77. Thank you for your thorough treatment of this issue! I experienced this problem and ended up wiping my hard drive and starting from scratch, but at least I don’t have a bricked computer. Didn’t loose too many important things… It is absolutely ridiculous that this is still an issue. Come on, Apple!

  78. Thank you so much for putting this together, after many hours I’ve made more progress this way than any other – but still not solved.

    2016 MacAir, booting from Mojave, open Disc Utility, confirms that space is the issue, but I can’t work out how to get to a position to actually delete any files to resolve the issue. I can mount the Macintosh HD – Data, but can’t find any way of “exploring” it to delete files, like Explorer etc. Tried right clicking all over the place!

    What is everyone else doing at this point?

    1. I fully installed Catalina to a second external drive (first one was the bootable installer as you’ve already done) and ran the OS directly from the external. From there I was able to unlock and mount the internal drive’s Data volume via Disk Utility. To be honest, I didn’t try to delete files to make enough storage for Big Sur, I just copied over the local files I needed to iCloud. Then I erased the internal drive and installed Catalina onto it from the bootable installer on the first external drive. From there I upgraded to Big Sur.

    2. I’m in the same exact spot. Eager to hear what others do here to delete data on the Macintosh HD – Data .

  79. Hi. I am stuck on target disk mode but it when accessing macintosh data-hd and it requires a password. I tried every password that is possible but it isnt working. Pls help me ): thanks a lot!

  80. Hi. I am stuck on target disk mode but it when accessing macintosh data-hd and it requires a password. I tried every password that is possible but it isnt working. Pls help me ): thanks a lot!

    1. Same thing! Would really appreciate if someone has a solution for this. Same thing with booting through an external drive. I cannot mount Macintosh Data – HD and can’t seem to decrypt it in any way.

  81. I just experienced an especially tricky version of this issue where even Target Disk mode wasn’t recognizing my drive so I decided to post in case others might be experiencing the same. Note: this method requires manually deleting large files using the Terminal to complete the installation and should probably only be used as a LAST RESORT. It would be a lot easier to boot in Target Disk mode then make some space by deleting files on the full disk using the other computer, but for some reason the disk wasn’t being recognized on the other computer even after trying everything (either because the Big Sur drive was corrupted or the disk was completely full at this point – DiskUtility showed only 17MB available).

    Here was my fix, which included manually deleting files to clear enough space (about 50GB) to complete the Big Sur update:
    1. Booted in recovery mode (holding Command (⌘)-R)
    2. Open Terminal from the Utilities menu.
    3. Deleted large unimportant files from terminal using “rm” command to create 50GB of free space (see https://apple.stackexchange.com/questions/197503/how-can-i-delete-files-in-recovery-mode-using-terminal-on-my-os-x-main-partition)
    4. Then, I confirmed that there was now enough space available on “Macintosh HD – Data” to finish installing Big Sur (other posts recommended 50GB so I went with that).
    5. At this point, you might be ok to just restart and hope for the best – however, this actually did NOT work for me (the computer continued to boot to the update progress bar then fail and shut down). It seemed to me that the Big Sur update installer had been corrupted somehow. At this point, I went back into Recovery Mode, then went through the steps to “Reinstall macOS Big Sur”.
    6. After reinstalling the Big Sur update with 50GB of available storage, the update finally completed and I got my computer back.

    Hope this can help someone else!

    1. Hi Albert, I wanted to try your solution as I had a same issue. But then when I rebooted in recovery mode (by holding Command & R) and went to the macOS Recovery, I couldn’t access terminal as it requires password. I don’t know why when I entered my password that I’m sure 100% correct, still didn’t work. Do you have any idea to fix this? Thanks!

      1. Hi Gerry, I never had to enter a password. Just try using “cd” to get to the correct directory. Is your disk encrypted? Where is it requiring password?

  82. You don’t need Mojave on another mac or external in order to recover data.

    Connect your mac to another mac via target disk mode. Assuming you did this correct and the cable is good you should get a pop up on the working mac asking for the password to unlock the disk for your broken mac. BUT the password is not going to work just yet.

    You need to go into Disk Utility and delete the “Macintosh HD” partition from broken computers HD. Once you delete this your password will then work to unlock the “Macintosh HD – Data” partition giving you access to your data.

    Not sure where the Mojave thing came from but the other mac you are using can be running any newer OS including Catalina and Big Sur.

    1. I have sort of learned some thing, which is mostly don’t do unnecessary updates and I knew that already! I had a difficult 2018 MiniMac which I think had File Vault on, a borrowed machine with El Capitan, trying to make bootable external hard drives, so was not having much luck of anything, I couldn’t always get to Terminal, or Recovery mode, it kept going to internet recovery instead, then I saw Jon’s post here and I was suddenly able to access my Data and Terminal, so I was able to save my important files, but must have done something wrong in Terminal when I was deleting files because now I can’t access anything, only internet Recovery mode, which just loops to the error triangle. I’ve tried the Bootable Big Sur and Mojave with no joy. It’s time to visit a clever friend with the proper kit and knowledge! Damn. I’m so shocked that Apple are so unhelpful and don’t seem to acknowledge this is their bug, and are so unwilling to even listen to the advice that is given here! Ridiculous. Thanks to all.. hopefully my machine is repairable!

  83. This is probably the only helpful information about this issue so I wanted to share my fix.

    I was able to get Target Disk Mode to work with the other laptop on Catalina; this will likely work for Big Sur too. I spoke to a senior agent at Apple and he mentioned that they are testing this out as a fix internally. Essentially the issue is that Big Sur is segmenting your data from your main drive into Macintosh-HD and now Macintosh-HD-Data and there is an incompatibility with your passwords on Macintosh-HD vs. Macintosh-HD-Data.

    Here are the steps:
    1. Set your Problem Mac into Target Disk Mode
    2. Connect it to your other Catalina device
    3. Unmount Macintosh-HD (this contains all the background processes and whatnot for Big Sur)
    4. Search for (or go to) Disk Utility
    5. Click the – button on Volume and click “Delete”to delete APFS Volume – DO NOT CLICK DELETE ALL
    6. Mount Macintosh-HD-Data and enter the password for your account from the Problem Mac
    7. Start deleting files to create space

    Other suggestions:
    1. Google Chrome was 17gb on my device; getting rid of that from Macintosh-HD-Data helped a lot
    2. You may run into permission issues opening files from your Problem Mac; make sure to enter the password from the Catalina Mac where possible
    3. You will regain space on your drive after the installation is complete

    1. Damn dude you are a life saver. I just followed your steps and this worked!! God bless you and happy Valentine’s Day!

  84. FYI the referenced tweet from Crsleeth mentions my article:

    https://blog.kylekukshtel.com/big-sur-update-failing-diskutil-apfs-filevault-sync-users

    The steps outlined above in MrMacintosh’s article didn’t fit my case — my drive had plenty of space when upgrading, but I had no access to an additional Mac that was able to be downgraded to non-Big Sur to test this on.

    I outline the fix above, but what worked for me was deleting the Macintosh HD data and Update partition in Disk Utility. This magically re-synced my credentials and then I was able to mount Macintosh HD – Data inside of Disk Utility. After that I copied all the files over via terminal to an external, and then wiped the machine and was able to do a clean Big Sur install from a bootable USB

    1. I definitly need some help, I deleted Macintosh HD in hope that it would magically reappear and fix my issue of the password not working…however this did not happen, and now Macintosh HD does not show up. When I boot in recovery mode and delete to reinstall Big Sur, it says ‘you may not install to this volume because it is invalid or damaged’ and tells me to use disc utility to erase the volume. Luckily I still have macintosh hd data, and I’m in the process of copy and pasting all my data to a USB so i don’t lose my data, I’m just worried because i don’t know how to reinstall onto my mac and start it as a new mac without macintosh HD.

      please help 🙁

  85. I was finally able to do it! I have a MacBook Pro 2018, T2 with Firevault enabled. I borrowed a MacBook Air 2018 with Mojave, bought a thunderbolt 2 cable and an adaptor (thunderbolt 3 to thunderbolt 2), and was able to open Macintosh HD – Data on the second computer, and recover all my data.
    I had tried earlier with a USB-A/USB-C adaptor, and it did not work (and I think they did the same in one of the shops that I went to).
    Thank you very much again for the elucidating article and all the comments that followed – I had been to several shops, talked to several technicians, talked on the phone with Apple support (we don’t have Apple store/geniuses in Portugal) – everyone told me that the data was lost, and that there was nothing to be done. The best of luck to everyone!

  86. I was FINALLY able to resolve this, without wiping my hard drive and losing all my data. You need another computer running OSX 10.13 or 10.14. Here’s the steps I followed (big thanks to https://mrmacintosh.com/big-sur-upgrade-not-enough-hd-space-serious-issue-possible-data-loss/)

    1. Plug problem laptop (2015 MBP with FileVault enabled) into desktop with thunderbolt cable, laptop in Target Disk Mode
    2. Desktop is running 10.15 Catalina. In Disk Utility, I see “Macintosh HD – Data – Data” which is the folder I need to access, but when I click Mount and enter my password, it is rejected. This is a problem with Catalina..
    3. Download OSX 10.14 Mojave
    4. Using the third party software DiskDrill I turned Flashdrive 1 into a bootable install disk of Mojave.
    5. Restarted Desktop holding Option key. Clicked install Mojave. Installed on 64GB Flashdrive 2.
    6. Booted from flashdrive 2.
    7. Opened Disk Utility, Laptop in Target Disk Mode, mounted Macintosh HD – Data – Data. Password works now!
    8. Deleted a bunch of files until I had over 30 GB free.
    9. Restarted Laptop, install finishes successfully!

    1. Hi i think we have the same problem. Password wont work when accessing the macintosh data-hd. How should i download osx 10.14 mojave? Thanks a lot!!!

    2. ^– This worked perfectly! A bit cumbersome but all data rescued from a botched install.

      How on earth did you come up with idea of downgrading to Mojave? Is it connected to the root cause for the issues with Catalina? I first tried to use internet recovery mode – but to no avail – I guess Apple serves Catalina recovery?

  87. I don’t have a second Macbook running on Mojave or High Sierra, and it looks like my Macbook is encrypted with FireVault, as my passwords are not being accepted in Recovery.

    My only option is to use my hard drive, but how do I install Mojave onto it? It’s currently plugged into my Macbook but there are no icons or indicators that I can access it- so how do I go about installing Mojave onto my hard drive?

    If someone has managed to do this already, please let me know!

    1. Hey Juliet, I just got my video up for a super detailed look at the issue. In your situation you are FileVault encrypted so you it all depends on what year your mac is. If you have a newer Mac you will not be able to boot to the external hard drive because of external boot protection. If you have a 2013-2017 you could install macOS on an external USB or hard drive and boot to that to get to your files. The only other option is to see if you can locate a friend that has a mac that could help. It no longer matters what OS they have on the Host Mac.

  88. This happened to me yesterday, trying to upgrade my MacBook Pro ~2016 from Mojave to Big Sur. I had around 32GB free in my disk (after downloading the installer). I went into recovery mode (powering off the computer, then holding down option and pressing power, kept holding down option until the logo appeared), where I could delete some of the files (it was shown a partition, Macintosh HD and Macintosh HD – Data, I could only access this last one). Once I was sure that I had deleted enough files (I did not believe what the Storage’s available space calculator was telling me, as it was for sure incorrect and inconsistent), I tried to upgrade again to Big Sur (it only allowed me to do it in Macintosh HD – Data). This worked for me. Hope it helps somebody else. Thank you for the post, it was super helpful!

  89. WOW – I was about to buy a new Mac Pro until I saw this article. Luckily I saved all my data to an external hard drive when the install started crashing saying I needed more storage capacity. I still don’t know how to erase my Mac and reinstall, but will figure that out or contact Apple to walk me through that process.

  90. Hi,

    I’m slightly confused where you say:

    If you have only your Mac:
    1. Remove files via terminal.app in macOS recovery.
    2. 2013-2017 ONLY – Use an external USB flash drive or external hard drive. You can boot your Mac to an OS on a external drive. You can then delete files from the external Mac desktop.

    This applies to me. Would anyone be able to walk me through this?

    Thanks!

    Tim

    1. Sadly Terminal doesn’t appear in the top bar for me – I’m guessing that 8should happen when in recovery.. no options for me there. Need to find another mac…

  91. It seems that I can only get round this problem with two macs.

    I have a hard drive, but every time I attempt to solve the issue by entering Target Disk Mode, I get two symbols, one for TDM and one USB symbol that just float around the screen.

    Can anyone help?

    Thanks

    1. I have a 2017 Macbook Air with this problem and I’m hoping to do a Target Disk Startup connection to my 2011 iMac. Neither have Thunderbolt 3 ports but they both have Thunderbolt 2, would this still work?

  92. Thank you very much for the helpful article and helpful comments. I had the same problem: I have a MacBook Pro from 2018, so I guess T2 Mac with firevault enabled. The solution offered on the article only works with High Sierra or Mojave? I took it to the shop yesterday, and they tried it with a second Mac with Big Sur installed, and they weren’t able to recover the data. If I tried with a second Mac with High Sierra or Mojave, would I be able to save my data?

    Also: I have a second Mac, late 2015, with Big Sur already installed. Would I be able to go back to the High Sierra or Mojave versions?

    I would be very grateful if you could help me on this.

  93. Issue solved here!
    Someone couldn’t boot anymore after upgrading to Big Sure with FileVault activated. He wasn’t stuck in a boot loop attempting to finish the install, but he had another error after booting and couldn’t reach the login window.
    He was able to start in recovery mode, from there we tried many “diskutil” commands from the Terminal to unlock and mount the “Macintosh HD – Data” partition, but they all failed.
    He tried the Target mode but couldn’t make it work, probably because he didn’t have the right cables.
    We ended up deleting the “Macintosh HD” partition (not the one with data)
    Then mounting “Macintosh HD – Data” from Disk Utility asked for a password, and it worked! Before deleting the partition, it was asking for a password too, but it never got accepted. I suspect deleting the partition holding the system files somehow removed a keychain file that was messing up the password authentication.
    Once the disk mounted, it was “easy” to go to Terminal, plug an external disk and copy all the data to the external disk with the “cp” command. (We tried to backup from Disk Utility creating a new disk image, but then the restore operation failed so we sticked to the Terrminal with “cp -av /Volumes/Macintosh\ HD\ -\ Data\ /Volumes/lacie/backup/”)
    Special thanks to Addi comment which helped a lot in taking this decision.

    1. Can you use charging cable for data transfer?
      Do it work on Catalina? As my second Mac has Catalina?
      Shame on Apple for letting it happen in first place 🙁

  94. Re: 13. How to fix this issue + retain your data!

    There’s a way to do it without a second Mac!

    My mid-2015 drive was 100% full during the update from Mojave to BS so I searched for a fix but no one has the same issue (FV enabled, HD 100% full, recovery mode could not see the Macintosh HD drives because original OS didn’t support APFS) and I don’t have access to a second Mac, so I used a 64GB SD card to install the original OS via internet recovery mode, then updating it to the same OS before BS via app store (just to be safe but any OS supporting APFS other than the buggy BS would be fine I guess). Then it asked for Macintosh HD data password and everything is accessible now.

    1. Hi Felix,

      I hope this works for me as well.

      What is internet recovery mode?

      At the moment, I’ve no idea how to escape the error and Target Disk Mode screen!

      Thanks,

      Tim

  95. MANY THANKS!! I was struggling with this. In my case I tried emptying some disk space, but the install didn’t succeed anyway. But at least I was able to manually back up data prior to erase/reinstall. 🙂

  96. I have the same problem. Macbook Air with FileVault Enabled. I tried target disk in iMac Pro with Catalina but the password is not accepted. I dont have a mac with 10.13 or 10.14.
    I have time machine backup so I just Erase and Reinstall.

  97. First of all, thanks for the great instructions.

    I used data transfer successfully to get enough space now (> 35gb). However, mac still goes into boot loop after entering the password. I understood from your instructions, it would continue installation. Any ideas?

    Thanks,
    Daniel

  98. Ah, I had exactly this issue yesterday. I could get into the system, but couldn’t do much; it looked as if Mojave had only been half-uninstalled, so there were two copies of things like System Preferences & Terminal, and System Preferences wouldn’t work, which meant I couldn’t grant permission to lots of things I might use to get out of the situation.

    I couldn’t repair anything from the Recovery partition because my FileVault password wasn’t working, so I presume I was also half-way through a FileVault upgrade.

    Fortunately, I was able to run SuperDuper from an external drive and make a clone (which of course I should have done before!) and then wipe everything, do a fresh install and migrate my data back from that clone.

    I wasn’t too distressed because it had been some time since that machine had had a good spring clean and because I had another Mac on which to do my actual work while this was happening. And, of course, because I had both SuperDuper and Time Machine. But if any of those had not been true yesterday…

  99. Would this work with a cable that connects my (no storage) MacBook Air 2017 (with no Thunderbolt 3 port) USB-A port to a MacBook with a USB-C port? When I go into target disk mode on my MacBook Air and connect it to the other MacBook (MacOS Mojave) using this cable, a pop-up window asking for an encryption password never comes up. I am not sure if I’m doing something wrong or if the cable is not doing it’s job. If so, would a Thunderbolt 2 cable work to connect my MacBook Air 2017 Thunderbolt 2 to another MacBook with a Thunderbolt 2 port? Any input would be appreciated.

  100. I GOT MY DATA BACK!

    I had this happen to me on Monday Feb 8th on my 2014 MacBook with Catalina. The update is suggested by apple, I did not seek it just like my phones I let it do its thing.

    Boots to recovery mode but does not accept the password and boots to target mode. Spent the day with the apple geniuses who tried everything with no luck. So I bought a new computer and left the store with my old one and wouldn’t let them reformat and reinstall.

    In target mode the drive did not mount on the new machine running Big Sur.
    Thanks to this column I was able try a friends machine that was running 10.14.
    From target mode the accounts showed up and once credentials accepted I was able to copy the data off.

  101. I have exactly this problem with a 2017 MacBook Air. Contacted Apple by phone but, dissapointedly, they gave me other solution than removing my data. In my city Apple premium resseller the same… she offered to reinstall but losing my data.
    Thank you, will try your solution in a few days

  102. Yes this is a very real and I think a a problem Apple’s OS team needs to make as there highest priority. Most users don’t have other Macs lying around and extra cables to do Target disk mode and most don’t know what that even is. Most users sadly do not backup their data before doing a Mac OS update or any update. Always assume like a toaster that it will always work perfectly. Unfortunately computers are not toasters. So although the workaround fix is great most don’t have the ability to even attempt it so sadly the only option available is to erase and install, start over. Apple needs to fix this now!

  103. Hi! Thanks for all your work on solving this maddening issue.
    So, my 2013 macbook which I’m quite certain have the FileVault encryption has only thunderbolt 2 connection and I want to try to connect it to a 2009ish macbook (running high Sierra) that only has Mini DisplayPort and old USB connections. Is this even possible since you said the only options for connecting is “USB-C to USB-C 3.0 Cable, USB-C to USB-A or a ThunderBolt 3 Cable.”?

    Thanks again for your work.

  104. This is really great write up. If I had found it a few days ago I would have waited on usb 3 A to C cable and tried target disk with a macos VM.

    2018 Mac Mini. My drive was mostly full. Never thought Apple would do an update without checking free space. I woke up to the failed overnight update. Preparing software.

    Booting into recovery did not show my user account to unlock and get to tools like Terminal.

    It just said “There are no users on this volume to recover”. Only options were restart and erase mac.

    Lost work I hadn’t pushed to github. Finally setup Time Machine after all this mess.

  105. if you have Mac that came with 10.12, 10.13,10.14, you can use SHIFT OPTION Command R to boot into original MacOS so that you might not need the 2nd Mac.

        1. Would this work with a cable that connects my (no storage) MacBook Air 2017 (with no Thunderbolt 3 port) USB-A port to a MacBook with a USB-C port? When I go into target disk mode on my MacBook Air and connect it to the other MacBook (MacOS Mojave) using this cable, a pop-up window asking for an encryption password never comes up. I am not sure if I’m doing something wrong or if the cable is not doing it’s job. If so, would a Thunderbolt 2 cable work to connect my MacBook Air 2017 Thunderbolt 2 to another MacBook with a Thunderbolt 2 port? Any input would be appreciated.

        2. Can you use Disk Utility to backup a partition that was encrypted with FileVault? I can’t figure out how to do this.

  106. Hey! Thank you very much for this comprehensive instruction.

    I am now stuck in step 13. My MacBook has filevault 2 enabled and luckily my old mac still has 10.13.6.

    I can access my files through target disk mode but I cannot delete anything. And I wonder how did you delete some files in the Macintosh HD – Data? I don’t want to erase my MacBook entirely.

    I checked “Get info”. On my 2nd MacBook, only admin(myself) can read and write the Macintosh HD – Data, staff and everyone are read only. I cannot change the status of any of three. Could this be an issue?

    Thank you very much for the help.

      1. Hello Mr. Macintosh, thanks so much for writing this blog post! I’ve gotten to the same step as Jason, I enter my password to access the drive of the machine in target mode, and I can see the folders, but they all have the red circle with the white line through them.

        Is there a way to get past this hurdle to delete the data or move it around?

  107. I have a mid 2012 mac pro running Catalina. Is it possible to do this method of getting. Big Sur. I a;ways get the message that the update is not avaliable.

    1. Hi there! I am trying to go through this process right now with my 2016 MacBook Pro. I have a second 2016 MacBook Pro running high Sierra 10.13.16. However, when I plug them together using (what I believe to be) an thunderbolt, the option to access my computer on the 2nd one does not come up.

      1. Same here, only my “other” mac has Catalina, 10.11.6 (15G22010). I plug them together with a USB / thunderbolt (i think) cable… and nothing appears

  108. If only this had been published a few days earlier, I wouldn’t have wiped my hard drive. I lost quite a bit of precious data. I’m glad this article exists and hope that it helps a lot of people.

  109. I was hit by this problem yesterday, on a T1 Macbook Pro with FileVault enabled.
    I was able to re-gain access to my encrypted Macintosh HD – Data partition by booting a macOS Catalina USB installer and then removing both the Macintosh HD and Updates APFS volumes via Disk Utility.
    When you delete the Macintosh HD partition Disk Utility will ask if you want to delete the Volume Group (which includes the Data partition) or just the APFS Volume and you should select just the APFS Volume, otherwise you lose the Data partition.
    After that you can now mount the Data volume with your FV password that didn’t work while the Macintosh HD volume was still there. Crazy, but it worked.
    I then copied the data off the computer to an external USB drive and reinstalled the OS.

    1. I did this as a last ditch attempt before clean installing and remarkably it worked! Thanks so much.

      I followed the steps in the article but I only had Big Sur (article says you need 10.14 or 10.13) available on another Mac. So I connected the Macs together with a thunderbolt 2 cable, booted the broken Mac via Target Disk Mode, opened Disk Utility and deleted the Macintosh HD but not the Data partition.

      Where previously it had constantly rejected my user password (in Recovery, Target Boot Mode and Big Sur install), it accepted it after the Macintosh HD was deleted.

      Thanks a lot for the article and comment.

    2. Thank you so much for this run through of what you did! This allowed me to grab my files off of my 2014 MacBook Air and onto an external drive before reinstalling Catalina on my internal SSD and then successfully upgrading to Big Sur from there.

  110. Thank you so much you saved my t2 filevault encrypted data!!!!! Copying data in target disk mode to another mac running mojave now.

    Funny that i went to the apple genius bar in Dubai Mall last week and they told me there is no solution to this. They wanted to erase my mac.

  111. Hello.

    In one case we could ONCE mount data-volume in Mojave, cleanup some space and… nothing but now it cannot accept password even in Mojave and High Sierra.

    Will try with other host machine.

  112. Thank you so much – after much searching, this is by far the clearest guide I found to resolving this critical issue (a OneDrive sync had filled up my disk just prior to attempting the upgrade)

    I am far from an expert, so the only thing I struggled with was using terminal in macOS recovery mode, I found this helpful in this regard: https://discussions.apple.com/thread/7940542

    Thanks again

  113. Hello
    Iam currently in the same exact situation.

    I have a Macbook pro 13″ 2018 version with T2 and filevault enabled. The Mac was running high sierra before I attempted to upgrade it to Big sur and the issue as described here happened, started with the error and now goes into the reboot loop. Password and icloud wont be accepted.

    Will your solution work? I only have an iMac mid 2013 as the 2nd mac to be used for recovery on which I can installed High Sierra or Mojave, but the question is which cable shall I use to connect the target mac with this iMac?

    Will the solution work? I need to recover my data.

  114. Thank you so much for this very thorough investigation, I’ve run into this problem and it’s been extremely stressful!

    I have the problem computer in target disk mode on a second mac, but in the Macintosh – HD -Data folder I’m not seeing any of my files (screenshot: https://i.imgur.com/4qzeIG6.png). I used the third party software Disk Drill and was able to access my files, although some of the older files were corrupted, so I’m still hoping to fix the problem properly and finish the install.

    The computer installing Big Sur is a 2015 MacBook Pro, without FileVault, running Catalina I believe, with about 25gb free space before downloading the Big Sur installer. It’s connected to a 2019 iMac running Catalina 10.15.7. You mentioned your solution working on 10.13 and 10.14, could the iMac’s OS be the problem? I was thinking of installing 10.13/4 on an external drive and trying that.

    Any other advice you could give? Thanks again!

    1. Kevin,
      Sorry for the confusion. I need to clarify a bit on which situations need a 10.13 or 10.14 Mac. This is only for encrypted Macs. If your Mac does not have FileVault enabled (like you said) you will not need to use 10.13 or 10.14. A 2nd mac with Catalina or Big Sur would be fine. Your situation is strange for sure. What you are looking at is actually the “Macintosh HD” volume NOT the “Macintosh HD – Data” volume. The Data volume is the one you need and is the one that stores your data. It does not make any sense that it’s mislabeled! When you plug in the mac does 3 volumes mount on the desktop like the picture in my article?

      1. I had this issue yesterday with one of our users. Macintosh HD – Data did not show up on the desktop. Only Macintosh HD was available.
        However, in Disk Utility you’ll see the Macintosh HD – Data volume. Perform a right click on it and select Show in Finder. You’ll then have access to your files.

        1. Have the same issue, can only see Macintosh HD – Data in Disk Utility, and it’s not mounted. How can I get into it? Try Mount or Restore? Thanks!

      2. We got the same problem on MacBook Air without FileVault. During first connection via Thunderbolt we could see files in Finder. But after re-connection volume Data was mounted fine but was empty. Right now we recover files by Disk Drill.

        Disk Utility said that “APFS has unknown feature”.

      3. You need a 2nd Mac running macOS High Sierra or Mojave. (Big Sur & Catalina Mac fix instructions coming soon).

        Do you happen to have instructions for Big Sur and Catalina? I tried connecting to a 2nd Mac with Catalina, but I’m pretty sure I have FileVault enabled so it didn’t work. But if have those instructions, that would be helpful. Thanks!

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