Time Machine backup fails due to insufficient space error

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Arthur7 Author

Level 1

4 points

Time Machine backup fails due to insufficient space error

Unable to backup with time machine as it gives error:

"Time Machine could not back up the disk “Macintosh HD” because it is nearly full.

Delete some files on this disk and try again."

Target disk is SSD formated to APFS (Case-sensitive, Encrypted), 1 TB with 391.72 GB available.

Changed target to another disc Mac OS Extended (Journaled), 1 TB with 805.75 GB available.

Ran Disc Utility/First Aid on both getting "Operation successful."

The target disk has been successfully used for at least two years and the alternate disk had been used previously.

Mac mini, macOS 14.7

Posted on Jan 17, 2025 11:12 AM

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Answer 1

John Galt

Level 10

148,086 points

Jan 17, 2025 11:51 AM in response to Arthur7

The exact wording of that message is important. If the source is named "Macintosh HD" and the message states "Time Machine could not back up the disk named "Macintosh HD" because it is nearly full" it is referring to the source volume.

Read this Discussion for an illustrated example: Time Machine unable to complete backup - Apple Community

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Answer 2

Tesserax

Level 10

153,390 points

Jan 17, 2025 1:22 PM in response to Arthur7

Just to add a bit to John Galt's reply ...

... at the beginning of a TM backup process, one of first things it does is create a local snapshot on the source volume. By default that would be Macintosh HD - Data (that's where all of your apps/data are stored.) If that volume is nearly full, TM will not be able to create that snapshot, and fail with that specific error message.

You can use Disk Utility to see those snapshots. To do so, be sure to enable "Show APFS Snapshots" on the utility's View menu. Then select your Data volume. The snapshots should then be listed at the bottom of the window.

Ref: Still struggling with snapshots - The Eclectic Light Company

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