Despite the irresistible rise of the SSD, I know that many of you are still making Time Machine backups to rotating hard disks. Although in recent versions of macOS they’re now in APFS format, so should be less prone to the errors which plague HFS+ backups, you still want to check your backup storage. Yet, when you try that in Disk Utility, all you see are errors or you have wait an age while every snapshot is checked. And Disk Utility won’t just check the backup disk, but insists on repairing it whether you want it to or not.
When Glenn Fleishman @GlennF raised the question of checking APFS backup storage, we recognised multiple conflicts:
• Although hard disks have become more reliable, they’re still prone to disk errors, so deserve periodic checks of the file system.
• APFS isn’t an ideal file system for hard disks; although backup snapshots are read-only, so relatively stable, most are also badly fragmented, and can’t be defragmented.
• Checking dozens or even hundreds of backup snapshots stored on hard disks can take many hours.
• If you don’t check the snapshots, there’s little point in checking your backup storage, as all your backups are stored in snapshots.
• As snapshots are read-only, if they develop errors, it appears that they can’t be repaired anyway.
• If a backup snapshot develops an error, there’s no way to replace it, as snapshots can’t be copied from another volume.Read more at eclecticlight.co