betaneptune wrote:
why does it take so long for First Aid to process the snapshots? Is it reading each byte a dozen times?
If you have a dozen snapshots, then yes. If you have 69, then it will take about 5 times longer than that.
Each snapshot is a self-contained file system. It contains only the file pointers and low-level block pointers. That's why the snapshot itself is so small. But each snapshot represents almost the entirety of the disk, with only very small differences between each snapshot. So yes, you are churning virtually your entire disk 69 times.
Is there some way to skip the snapshots? Maybe by using the fsck_apfs command in Terminal? (NOTE: This is a backup disk, not the system disk [startup disk], so I can't delete them, as they are the actual backups!)
The only way to skip them is to delete them. You could delete all but the last one. People have an unnatural affinity for the history of their backups. It's a nice trick that Time Machine has. You can usually recover files that you created in May and then deleted in June. But that requires the historical data. If you're concerned that your power outage has corrupted the disk, then you don't really have any options, as long as you insist on preserving that data from May.
If you value your backup drives, you have to keep them on UPS. A better idea is to have multiple drives and don't keep all of them connected all of the time.
Also, APFS is supposed to be more resilient to standard types of corruption. I regularly get "disk ejected" warnings when no disk has been ejected, and it doesn't seem to cause any harm.
