Time Machine snapshot could not be created for the disk "%@"

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Level 1

11 points

Time Machine snapshot could not be created for the disk "%@"

I just upgraded my iMac (Retina 5K, 27-inch, Late 2014) to Big Sur. All went well, except Time Machine now will no longer create a backup.

I get the error: "Time Machine could not back up the disk "%@" because a snapshot of the disk could not be created."

I have about 87GB free on my single 1TB Fusion Drive.

After some googling, I have tried:

a. Run Disk Utility First Aid on the Fusion Drive (and again on the contained volumes - no issues).

b. Deleted old local snapshots - to free up space (tmutil listlocalsnapshots / etc.).

c. Confirmed I could manually create a new snapshot (tmutil snapshot).

d. Tried using a new Time Machine backup disk (no difference, as I assume the issue is happening before it actually backs up to the backup disk itself).

I suspect the key to the problem is the disk "%@" that Time Machine is apparnetly trying to create a snapshot of.

What is disk "%@" ? It sounds like a bogus disk reference? (which might explain why a snapshot could not be created).

I'm not sure what to try next?

Posted on Nov 17, 2020 12:12 PM

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Answer 1

Best reply

KimballLarsen

Level 1

13 points

Nov 24, 2020 9:57 AM in response to KimballLarsen

Ok, I resolved the issue, and Time Machine is now backing up correctly.

To recap: This computer never had Catalina on it. Went straight from Mojave -> Big Sur. After upgrade to Big Sur, no Time Machine backups would work at all (to external USB hard drive or to a network store). They all failed with a message like "Time Machine could not back up the disk "%@" because a snapshot of the disk could not be created."

On the misbehaving machine, I had to remove the /Volumes/com.apple.TimeMachine.localsnapshots directory. This is a hidden directory, but you can delete it via the terminal if you have sudo or root permissions. I noted that in this directory were some snapshots from *before* Big Sur was installed.

sudo rm -r /Volumes/com.apple.TimeMachine.localsnapshots

Once that was deleted, I also deleted all the local snapshots using this terminal command (note that this listed and deleted snapshots from *after* Big Sur was installed:

sudo tmutil deletelocalsnapshots /

As soon as I did both of the above, Time Machine started working correctly.

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Answer 2

bpmd

Level 1

8 points

Nov 22, 2020 6:52 AM in response to MyersCarpenter

I'm having this same problem on my 2017 iMac. This is from the Console app:

Illegal permissions or ownership discovered on local snapshot directory!

Failed to mount stable snapshot: com.apple.TimeMachine.2020-11-22-090417.local source: Macintosh HD - Data

Failed to create or mount stable snapshot.

Backup failed (49: BACKUP_FAILED_MOUNT_LOCAL_SNAPSHOT)

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Answer 3

Nov 24, 2020 9:34 AM in response to t-mac-support-community

I'm running into the exact same issue, trying to backup a machine which was upgraded directly from Mojave to Big Sur (skipped Catalina) to a Synology Disk Station. Other Big Sur macs which were upgraded from Catalina have no problem backing up to the same destination.

I'm betting the problem is related to permissions on the local snapshot directory.

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Answer 4

KoolKiwi Author

Level 1

11 points

Nov 21, 2020 5:04 PM in response to nicolasfromgembloux

Hi. Firstly, thank you for the reply. It's great to know that this new Big Sur upgrade issue is not unique to me! :)

After much searching and trying different things, I finally gave up on finding a quick solution (no doubt there will be one).

I also reviewed a few of the 3rd Party Backup solutions, thinking of just ditching Time Machine.

But in the end I took the more brute force approach of a clean install of Big Sur.

To achieve this (without my Time Machine backup to recover from), I grabbed a spare 2TB USB drive that I had, and also a 16GB SD Card.

I then created a Big Sur installer disk on the SD Card, and clean formatted the USB Drive.

I then booted from the SD Card and created a clean Big Sur installation on the external USB Drive, which included Migrating all my data across from the internal Machintosh HD - Data drive.

Once complete this gave me the confidence of a full back-up, on an external drive, that I could boot-up from (if all else failed).

However, when the migration was successfully complete, instead of signing in to my replicated external boot drive, I instead shutdown and again booted into the SD Card Big Sur installation disk.

I then proceeded to completely erase my internal 1.12TB Fusion Drive (note this also required me to then recombine the resulting seperated / formatted 1TB disk0 drive and 121GB disk1 SSD drive, to re-establist the combined 1.12TB empty Fusion drive - an easy terminal diskutil command).

Finally, as I first did above with the External drive, I now created a clean Big Sur installation on the cleanly formatted internal 1.12TB Fusion Drive, specifying to migrate my data back from my attached USB Drive.

Once this was all completed, I shutdown and removed the SD Card & USB Drive, then rebooted and signed back into my newly installed and recovered internal Fusion Drive, re-signed back into iCloud, and after a short while of disk activity I have everything back and a seemingly snapier machine! :) (Note: This would be my first "clean OS install" since continuously upgrading the OS since I bought the iMac new in late 2014).

Of course, the final step was then re-activating Time Machine, to again start backing-up to my also cleanly erased Time Capsule. This all now worked flawlessly. So, original problem solved! :)

Note that with a nearly full 1.12TB Fusion Drive this process took about 8 hours to create the replicated USB3 connected bootable system Drive, but only around 4 hours to then re-create and replicate everything back to the Internal Fusion Drive.

In summary, although I have no idea what the cause was (or a more direct fix is), for the original "Time Machine could not back up the disk "%@" issue, I'm actually very happy with the way I resolved this. Because I now have the satisfaction of a cleanly installed Big Sur OS, with all of my accounts and data restored and a snapier "cleaner feeling" system.

But of course, you need to make your own choices on how to resolve your own issue, as (of course) YMMV.

Hope this is helpful.

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Answer 5

Nov 21, 2020 11:58 PM in response to KoolKiwi

Hi,

Thank you very much for your long and fast reply. It's very appreciated!

Something very strange happened from my side. The day after, without doing anything, time machine error disappeared and started working like a charm...

Can't explain what happened but so far so good.

Just to let you know, my time machine device is a 2TB Western Digital USB disk connected via USB to an old AirPort Extreme station and I am running a Late 2018 MBP.

Hope you will enjoy you newly installed Mac OS.

Cheers,

Nicolas

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Answer 6

KoolKiwi Author

Level 1

11 points

Nov 22, 2020 12:32 AM in response to nicolasfromgembloux

Hi Nicolas. Thanks for the update. Interesting that your issue fixed itself the next day.

I only did my full re-install yesterday, after a week of trying everything I could find / think of, which also included multiple reboots etc. over the week. Same Time Machine backup error all the way through.

I had also tried a USB disk for Time Machine, as well as my Time Capsule. But the error was happening before anything was being writen to the backup disk. ie. It was an error with the initial pre-backup local disk snapshot (on a strange disk "%@" reference).

Hopefully someone can find a definitive answer on how to fix the problem, as I see a number have flagged as also having the problem?

But, yes, I'm really happy after going ahead with my full OS re-install solution. :)

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Answer 7

Nov 22, 2020 5:19 AM in response to KoolKiwi

I think the "%@" is a bug. It's used in the programming languages that Apple uses (Swift and Objective C) to say "put this variable in this string. I think they just forgot to put the disk name there.

If you look at the Console app right after this happens do you see any error messages that might help?

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Answer 8

Nov 22, 2020 8:33 PM in response to KoolKiwi

I'm having this same issue when trying to backup to one of my Time Capsules. Always worked fine in Mojave, just upgraded to Big Sur yesterday. I tried erasing the disk, no change. Any other suggestions?

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Answer 9

KoolKiwi Author

Level 1

11 points

Nov 22, 2020 9:40 PM in response to Tim Schlack

Hi Tim. See my long post on how I resolved my issue (and also got a significant performance boost), by doing a full disk erase and clean Big Sur install.

The latest comments suggest it may be an authorities issue. Have you checked the console log messages to see if the same is happening for you? If so, perhaps look up how to reset authorities via recovery? My issue is now resolved, so I can’t try this myself to see if it’s a fix.

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Answer 10

Nov 23, 2020 5:05 PM in response to Tim Schlack

Hi Tim,

That is interesting as I also upgraded straight from Mojave to Big Sur. I have been assuming it is a permissions problem but neither FirstAid or "diskutil resetUserPermissions / `id -u`" have helped.

I get the same error on either a local USB or on the NAS. If nothing gets resolved with the next point release I will do the same as KoolKiwi

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Answer 11

Nov 24, 2020 9:16 AM in response to KoolKiwi

Mid 2015 MacBook Pro 15". I'm having the same issue, same error message after Big Sur upgrade. Time Machine was working fine before upgrade. Disk Utility First Aid says external drive if fine. Just to be sure I erased and reformatted it. Tried a variety of APFS formats, all failed. Oddly enough my 2018 MacBook Pro was also updated to Big Sur and Time Machine is working as expected. Working with Apple Support escalation team to get an answer. Right now they are moving it so some higher level engineers. I've given them a link to this forum topic. I'll report back if I learn anything.

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Answer 12

KoolKiwi Author

Level 1

11 points

Nov 24, 2020 9:55 AM in response to t-mac-support-community

For what it's worth, although I didn't mention it in my original post, I also had skipped Catalina, and was upgrading directly from Mojave to Big Sur. So this does appear to be a common cause!

Also, regarding the above comment: "Disk Utility First Aid says external drive if fine. Just to be sure I erased and reformatted it."

Note that the reported error is during the creation of the disk snapshot, which I understand is before data is written to your external Time Machine backup drive. Therefore, applying Disk Utility First Aid to your external drive and/or reformatting it, is not where the problem lies. The problem is with the creation of a snapshot of, and on, your internal Mac OS drive.

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Answer 13

Nov 25, 2020 8:08 AM in response to t-mac-support-community

I tried KimballLarsen Terminal solution but couldn't get it to work. I was able to delete the local snapshots but sudo rm -r /Volumes/com.apple.TimeMachine.localsnapshots said I didn't have permission to do that action. Glad it works for others.

I did hear back from Apple. They have acknowledged that there is a problem and they are looking into it and will likely include a fix in an upcoming MacOS update.

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Answer 14

Poet1803

Level 1

9 points

Nov 27, 2020 12:52 PM in response to KoolKiwi

Hi. I think I follow your route back to a functioning Time Machine! I have exactly the same problem on my 2015 Macbook Pro 13. Please, how did you reformat your internal drive? Was this done when you ran the Big Sur installer? Cheers, Ian

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Answer 15

Poet1803

Level 1

9 points

Nov 27, 2020 3:41 PM in response to BDAqua

Hi, thanks for the reply. I have just upgraded my Macbook Pro 13 to Big Sur which is what had caused the Time Machine glitch. But it’s all sorted now! I ‘chatted’ with an Apple specialist online and he helped me sort it by simply creating a new user account which I called Test. As soon as I logged into the new account, I saw that Time Machine had started backing up to my Time Capsule. When I switched back to my account, the backup was still running. So, doing that seemed to sort out the problem with the local snapshots. Certainly much safer and easier than messing about in Terminal! Hope this helps anyone else with the same problem.

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Time Machine snapshot could not be created for the disk "%@"

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