How to repair a snapshot with an error when it’s one of your backups on a hard disk? Currently this seems impossible, putting all those backups at risk.
First Aid
Don’t waste time trying to discover which files are still open when you want to check or repair an APFS disk and Disk Utility throws an error. Here’s the solution.
When your backups are stored on hard disks, even though they may use APFS, it’s important to check they’re sound. How to do better than Disk Utility.
APFS is almost 4 years old, and set out to solve the problem of accumulation of minor errors which has plagued HFS+. Has it?
Although generally reliable in normal macOS and in Recovery, First Aid sometimes runs into problems with external bootable disks.
Apple says that if you run First Aid on a disk, each of its volumes is checked too. Is that really true?
The Eclectic Light Company 