EXPERT ADVICE
Our resident genius solves your Mac and iOS problems
Fix a First Aid flaw
since Apple introduced its S new file system APFS, running First Aid on its volumes and containers has been a gamble. More often than not, checks fail with status 65, and we’re advised to back that volume up as if its failure was imminent. This is most worrying when that volume contains dozens of Time Machine backups.
It turns out the problem lies not in the volume being checked, but in macOS. Disk Utility relies on the command tool fsck_apfs to run these checks and perform any repairs needed, and that requires the volume and its container to be unmounted first. Although regular volumes may unmount fine, snapshots often prove impossible, so fsck_apfs can’t run any checks, and returns error 65.
Manually unmount an external disk before running First Aid and success becomes far more likely.