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Time Machine automatic backup no longer working - error message: "The backup disk image could not be created."

Since upgrading too macOS Big Sur my Time Machine backup process has stopped working across all of my devices.


I've been able to successfully backup manually using an attached USB drive, but the automatic backup over wifi, which I've been using successfully for the past several years, no longer works.


Error message I get is "Time machine couldn't complete the backup. The backup disk image could not be created."


I've taken the following steps to try and resolve this issue myself:

  • I've restarted all associated devices (laptops, NAS, etc).
    • I've turned off time machine, restarted, turning time machine back on, etc
  • I've created a new backup folder and restarted time machine
  • I've tried these steps on two different laptops (both were updated to macOS Big Sur at the same time)


I'll continue to backup manually, but if anyone has an idea of what I could try to get the automatic backup process working again would be greatly appreciated.


16" MacBook Pro, MacBook Pro 16″

Posted on Nov 28, 2020 5:20 PM

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Posted on Dec 4, 2020 8:19 AM

If you are using Sophos Home, it causes issues with Time Machine backups to a NAS. Sophos is aware of the issue: https://support.home.sophos.com/hc/en-us/articles/360051251412-Support-for-macOS-11-Big-Sur-

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5 replies

Nov 29, 2020 6:20 AM in response to John Galt

Hi John,


Thank you for taking time to reply, however while your comment was not helpful, it is also inaccurate.


Since Apple no longer makes a NAS device, your suggestion is not possible. Unless your suggestion was to use an AirPort Time Capsule (which was discontinued in 2018) to solve my issue?


If you'd like to learn about the Time Machine feature before replying, I'd refer you to Apple's Time Machine support page (https://support.apple.com/en-us/HT201250).


Nov 29, 2020 6:46 AM in response to bwalther

All my network TM backups use Apple AirPort Time Capsules and Apple AirPort Extreme Base Stations. They have been 100% reliable since the inception of Time Machine well over a decade ago. Not one failure to back up or restore.


Non-Apple NAS devices have never been, nor will they ever be reliable with Apple's Time Machine. Peruse this site for hundreds if not thousands of reports similar to yours. If you want to use a non-NAS device for backups then use something other than Time Machine. Otherwise I look forward to your report of success. It will be temporary.

Time Machine automatic backup no longer working - error message: "The backup disk image could not be created."

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