Snapshots made by Time Machine and tmutil should be purgeable, although sometimes they won’t purge, and aren’t shown reliably as purgeable space. An exploration of bugs and missing documentation.
snapshot
Demonstrated 10 years ago as a major new feature in APFS, and capable of blazingly fast rollback preserving data including document versions, snapshots still aren’t fully accessible or documented.
Can be a Mac-saver if you have problems when your backup storage isn’t available. You don’t need to run Time Machine to make them, and can roll back in Recovery, as shown here.
Should you attempt a repair in Recovery mode? Is it just a warning? How to identify the file or folder with a problem, and what to do to fix or prevent it from recurring.
As Time Machine has changed, first to back up APFS volumes, then to create backups as snapshots, its needs have changed. This makes it complicated to decide which local snapshots you can delete without affecting its backups.
Fundamentally simple: a preserved copy of a volume at a moment in time. How its size can only increase with time, how they’re managed, what they’re used for, and the tools for using them.
Why upgrading to Tahoe shouldn’t consume the last free space on your Mac’s SSD, and once it has settled should use little more than currently. How to clear out old snapshots and reduce System Data.
If you’ve got large files like Virtual Machines or media libraries on the Data volume on your Mac’s internal SSD, use this method to keep the size of its snapshots smaller.
Backups don’t include everything. Here are details of those items excluded from Time Machine backups, and why they’re excluded.
What disk checks are made in Safe mode? How are they different from those run during normal startup? If Disk Utility is to be our only APFS repair tool, shouldn’t have more and better features?
The Eclectic Light Company 