Intermittent Time Machine problem on Big Sur: snapshot of the disk could not be created.

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Level 1

4 points

Intermittent Time Machine problem on Big Sur: snapshot of the disk could not be created.

About once every 24 hours, max about 48 so far, I get this error message:

Time Machine could not back up the disk “2TB Drive” because a snapshot of the disk could not be created.

I'm now running Big Sur but before that, in the last two or three months, I used to occasionally get the same message on Catalina but only roughly once every two or three weeks.

As far as I can tell this seems to be a different problem from similar posts here.

I've tried: running a Disk Utility check on both disks involved (both checked out OK); restarting in Safe Mode; creating a new account and logging in from that; deleting existing snapshots.

But the only thing that works is restarting the computer, which usually solves the problem for about a day with backups working normally until the next time the error message pops up.

I have a terrabyte of free space on my Macintosh HD, so that can't be the problem.

Any ideas?

iMac (Retina 5K, 27-inch, Late 2014)

iMac Line (2012 and Later)

Posted on Dec 26, 2020 4:22 AM

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Answer 1

W A Mozart Author

Level 1

4 points

Dec 26, 2020 4:34 AM in response to W A Mozart

I should add that until the latest error message the exact wording read:

Time Machine could not back up the disk “%@” because a snapshot of the disk could not be created.

I'd assumed that “%@” was meant to read Macintosh HD.

2TB Drive is my external drive.

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Answer 2

W A Mozart Author

Level 1

4 points

Jan 12, 2021 1:09 AM in response to W A Mozart

Still happening. On just two occasions the disk cited in the error message was "2TB Drive", but otherwise it's “%@”.

Does the fact that both disks have been affected point to a Time Machine software problem rather than anything wrong with either disk?

Occasionally restarting the computer has made the message go away for two or three days, but usually it pops up again in 24 hours or less. In between, the backups are working normally.

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Answer 3

W A Mozart Author

Level 1

4 points

Jan 28, 2021 7:20 AM in response to W A Mozart

Something has changed. Since a couple of days ago, the error message has appeared once an hour two or three or more times, but then without restarting the Mac, normal Time Machine backups have resumed of their own accord.

I wonder if this is anything to do with the last time I restarted, when I decided to select Shut Down instead of Restart. The Mac didn't shut down, but instead restarted of its own accord, with the Message "Your Mac was restarted because of a problem…". After that I selected Shut Down again, and it shut down normally.

Curiouser and curiouser.

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