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Time Machine couldn’t complete the backup to “TimeMachine”. An error occurred while preparing the backup

I've been getting this error for a while now. Yes, I saw the article, and I've reformatted my external disk, reselected for Time Machine Backup, Completely reformatted. Over and over. Rinse wash repeat. Nonetheless I continue to get this nondescript error with NO error code to assist with troubleshooting.

Apple continues to point to the same article but NONE of those steps seem to help.

I suspect a bug in Big Sur. It'd be nice to receive an ack of some kind.

11.5.1

Mac Mini 2018

Disk

5TB External Drive

USB

Mac mini, macOS 11.5

Posted on Aug 2, 2021 9:26 AM

Best reply

DiZoE

Level 4

2,931 points

Posted on Aug 25, 2021 9:04 PM

Hey there! For this, I may, as I posted before, (Appears the OP’s cause was something different, due to the logs), I would:

Disconnect any external drive you use for Time Machine, (Eject first).

Turn OFF Automatic backups in System Preferences > Time Machine.

Open Terminal in Finder > Applications > Utilities.

Paste this command to clear the Time Machine snapshots, and press Return afterwards.

sudo tmutil thinlocalsnapshots / 999999999999999 4

Once it finishes, Restart, re-connect the external drive, re-enable Time Machine and test again.

PS: Before running the command, also delete the incomplete backup in Finder:

Double click the external drive on the Desktop, or in the Finder Sidebar.

Open “Backups.backup”, open the name of your Mac, scroll to the bottom, (Usually), and move the tile of the incomplete backup, “Usually says In Progress”. Then try the steps above.

Otherwise, how is your Mac and external drive’s storage? Hope that helps!

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Time Machine couldn’t complete the backup to “TimeMachine”. An error occurred while preparing the backup

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