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

You are watching: You may not install to this volume because it is currently being encrypted

What are the reported problems with this update?

1. Big Sur Upgrade stuck in an install loop2. Stuck in recovery Boot Recovery Assistant. Pop up error – An error occurred preparing the software update – An error occurred applying the software update3. 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 – Confirmed2. Big Sur 11.2 – Confirmed3. Big Sur 11.1 – Not affected4. 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.

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.

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.

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

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 stevemasermentioned 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 13GB1. 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 15GB1. 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.

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.

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.

RecoveryTarget 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.

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.


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 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)


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.

2013-2017 Mac – FileVault 2 Encryption Not Enabled2013-2017 Mac – FileVault 2 Encryption Enabled2018-2020 Mac – FileVault 2 Encryption Not Enabled2018-2020 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.

You can boot from this external version of macOS. This will allow you to clear enough space from “Macintosh HD – Data”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

You need a 2nd Mac running macOS High Sierra or Mojave. (Big Sur & Catalina Mac fix instructions coming soon)One of the following cables are required. USB-C to USB-C 3.0 Cable, or a ThunderBolt 3 Cable.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.

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

Author Mr. MacintoshPosted on February 8, 2021March 17, 2021Categories #MacAdmins, 10.14 Mojave, 10.15 Catalina, 11.0 Big Sur, Big Sur Upgrade Free Space Issue, macOS Big Sur 11.2, macOS Installer, macOS Upgrade, Recovery Partition

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

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.

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.

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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?

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.