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Question: Time Machine Backup Fails Because 4.43 TB of Data on a 1 TB Drive Changed?

Time Machine successfully backed up my computer yesterday (May 27, 2018) at 5:43PM, or so it says. Starting about an hour later, Time Machine started reporting that backups were failing. The exact message is:

User uploaded file

Important facts:

  • Macintosh SSD (boot volume) is an APFS-formatted 960GB solid-state drive with only 545.5GB used.
  • Time Machine HD is an HFS+-formatted 2TB mechanical hard drive.
  • I have run Disk First Aid on both volumes, and no errors were found.
  • Time Machine says the estimated size of a full backup is 511.5GB.
  • I have not restored any files since the last successful backup.
  • I haven't touched anywhere near 4TB of data since the last successful backup.


I did have an SMB volume mounted when Time Machine started reporting this error, but you can't add an SMB volume to the exclude list (and besides, Time Machine isn't supposed to back those up anyways).


Why is Time Machine trying to backup over 8x more data than is presently on my computer? And how can I get Time Machine to rediscover what it needs to backup, preferably without having to format my current Time Machine volume, or without having to buy a larger Time Machine volume?

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Answer:

I found the reason: an application that crashed between the last successful and first failed Time Machine backup had apparently created a 4TB sparse image in its Application Support directory.


That would explain why my system drive isn't full, yet Time Machine wants to back up way more than my system drive could hold.


Once I found the sparse image (command line: cd /; find . -size +1T) and added the application's Application Support folder to Time Machine's exclusion list, Time Machine was able to successfully run a backup.

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Question marked as Solved

May 28, 2018 12:59 PM in response to jdmcs In response to jdmcs

I found the reason: an application that crashed between the last successful and first failed Time Machine backup had apparently created a 4TB sparse image in its Application Support directory.


That would explain why my system drive isn't full, yet Time Machine wants to back up way more than my system drive could hold.


Once I found the sparse image (command line: cd /; find . -size +1T) and added the application's Application Support folder to Time Machine's exclusion list, Time Machine was able to successfully run a backup.

May 28, 2018 12:59 PM

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Question: Time Machine Backup Fails Because 4.43 TB of Data on a 1 TB Drive Changed?