Fix macOS "Time Machine" Disk Full
Time Machine says "Backup Failed" because the disk is full, even though it's supposed to delete old backups?
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The Symptom
Error message: "The backup disk is full. Time Machine could not complete the backup."
The Fix
- Manually Thin Old Backups
Find your backup drive name and run:
tmutil thinlocalsnapshots / 10000000000 4
- Verify the Backup Disk
diskutil verifyVolume /Volumes/[BackupDriveName]
- Reset Time Machine Preferences
sudo rm /Library/Preferences/com.apple.TimeMachine.plist
Then re-select your drive in System Settings.
Pro Tip
Time Machine needs a disk at least 2x the size of the data you are backing up to handle the rotation of old files effectively.