Time Machine vs APFS Snapshots
Plenty of people believe they have no backup because no external drive is connected. Their Mac has been quietly taking hourly snapshots the whole time. Those snapshots are useful, they aren't a backup, and the difference matters.
Since APFS arrived, Time Machine has done two separate things that get confused with each other.
The two mechanisms
Time Machine backups
Copies of your data written to a different physical device: an external drive, a network volume, a Time Capsule. Survives disk failure, theft and liquid damage, because the copy is somewhere else.
APFS local snapshots
Point-in-time references stored on the same internal drive, taken roughly hourly whenever Time Machine is enabled, whether or not a backup destination is connected. Retained for about 24 hours and thinned automatically when space runs short.
A snapshot isn't a copy. It is a record of what blocks looked like at a moment in time. Unchanged data is shared with the live file system rather than duplicated, which is why snapshots start cheap and grow as files change.
What snapshots are good at
- Recovering a file you overwrote or deleted earlier today.
- Rolling back a failed macOS update, which is why the installer takes one first.
- Entering Time Machine and browsing back through the day with no external drive connected.
That last one surprises people. Open Time Machine with no drive attached and you can often still restore from earlier the same day.
The storage cost
This is where snapshots collide with the storage confusion covered in purgeable space. Snapshots can hold many gigabytes, macOS counts that as available because it can reclaim it, and third-party tools count it as used.
See what you've:
tmutil listlocalsnapshots /Ask macOS to free roughly 10 GB of it:
sudo tmutil thinlocalsnapshots / 10000000000 4The final number is urgency, where 4 is the most aggressive. Usually you shouldn't need this. Worth knowing when an installer insists there's no space while Finder claims there's plenty.
Turning them off, and why you probably shouldn't
Local snapshots stop if you disable Time Machine entirely, which also stops real backups. That trade is rarely worth it. macOS already thins snapshots under pressure, and the protection they provide against your own mistakes is valuable.
If you're chronically short of space, the fix is a bigger drive or fewer files, not disabling a safety net.
See what your snapshots are holding
CleanMachine lists APFS snapshots with real sizes and creation times, so you can tell the difference between snapshots and files when storage gets tight. Free to scan.
↓ Download Free & ScanWhat a real backup strategy looks like
- Time Machine to an external drive. Cheap, automatic, and it survives your internal disk failing.
- An offsite or cloud copy for anything you can't recreate. Fire and theft take the Mac and the backup drive sitting next to it.
- Local snapshots as a same-day undo, which you already have.
Snapshots are layer three. Treating them as layer one is the mistake, and it is an easy one to make because macOS never explains that they exist.