Your Time Machine back-up disc may not always be available, so Time Machine also stores some of its back-ups on your Mac. These back-ups are called local snapshots.
How to use local snapshots
When your back-up disc isn't available, Time Machine automatically uses local snapshots to help you restore files. Reconnect your back-up disc to make even more back-ups available.
How local snapshots use storage space
You don't need to think about how much storage space local snapshots are using, because they don't use space needed for tasks like downloading files, copying files or installing new software.
Your Mac counts the space used by snapshots as available storage. Even so, Time Machine stores snapshots only on discs that have plenty of free space, and it automatically deletes snapshots as they age or as space is needed for other things.
If you want to delete local snapshots manually, turn off Time Machine temporarily:
- Open Time Machine preferences from the Time Machine menu in the menu bar. Or choose Apple menu > System Preferences, then click Time Machine.
- Deselect "Back Up Automatically" or click the Off/On switch, depending on what you see in Time Machine preferences.
- Wait a few minutes to allow the local snapshots to be deleted. Then turn on Time Machine again. It remembers your back-up discs.
How often local snapshots are saved
Time Machine saves one snapshot of your startup disc approximately every hour, and keeps it for 24 hours. It keeps an additional snapshot of your last successful Time Machine back-up until space is needed. And in macOS High Sierra or later, another snapshot is saved before installing any macOS update.