What can you do with Time Machine backups on APFS?

When Time Machine made its backups to an HFS+ volume, there was a great deal you could do with those backups and their storage, including making a complete copy of them, and deleting large items from inside a backup. This is because those backups were basically just a structured set of files, folders and hard links.

Now that Time Machine is making its backups to an APFS volume in Big Sur and later, those backups have changed, becoming synthetic snapshots, which aren’t amenable to the manipulation you could perform on an HFS+ volume. This has left many users puzzled as to why these new backups don’t work ‘properly’. This article explains what they can do, and what they can’t, things that Apple doesn’t tell us, and even Apple Support seems worryingly vague about.

What you can do

Restore individual items
In the Time Machine app, move back to the backup you want to restore an item from, select the item, and click on the Restore button at the bottom. If that item already exists in the location that you’re restoring it to, you’re given options as to whether to keep both copies or replace one. You can also do this in the Finder. Open the Time Machine backup you want to restore from, and simply drag the item across to the folder on your Mac you want to restore it to. If that item already exists there, you’re given options as to how to handle that. Many apps also let you restore their documents from Time Machine, from within the app.

Restore a whole volume
In the Time Machine app, you can select the correct volume in the right backup and Control-click to bring up the contextual menu, which offers the Restore [name] to… command. You may also be able to do this in Recovery mode, using the Restore from Time Machine Backups utility, although that may instead offer to migrate rather than restore, depending on the circumstances.

Migrate from a backup
Use Migration Assistant to do this, either by opening the app from the Utilities folder, or in a migration from Time Machine backups in Recovery mode. This gives you control over which folders and items are migrated.

Delete a whole backup
Although you could do this in the past in the Time Machine app, that’s no longer available when backing up to APFS. You can still do this in the Finder, though. Open your backup volume in the Finder, select the backup you want to delete, Control-click on it to bring up the contextual menu, and you’ll there see a command to delete it immediately. Be very careful though as this doesn’t work through the Trash; once deleted, there’s no way to recover that backup. You can also delete the backup from the list of snapshots in Disk Utility, or using the command
tmutil delete -d /pathToBackupStore -t backupTimestamp
where pathToBackupStore is the full path to the backup storage, and backupTimestamp is the timestamp name given by
tmutil listbackups
These commands may need to be run using sudo, and are explained in detail on Der Flounder.

Delete all your backups
The quickest and simplest way to do this is to erase the backup volume in Disk Utility. You can trash all the individual backups, but that may take an age to complete, and provides no benefit. Be careful to ensure that you select the correct volume, and remember that this is completely irreversible: once they’re gone, they can’t ever come back.

What you can’t do

Delete items within a backup
The synthetic snapshots containing your backups are read-only. As a general principle, you can never change an APFS snapshot, and Time Machine’s backups are no exception. This can cause problems when a volume being backed up automatically by Time Machine contains temporary large files, as may occur when you download very large installers such as IPSW images. See the section below for details on how you can manage this.

Transfer or copy the backups
Although Time Machine itself copies a snapshot over to the backup volume and uses that to assemble the data required for it, there’s currently no way that you can copy or move snapshots from your backup storage or anywhere else for that matter. It’s possible but complex to make a block-level copy of an entire disk at the command line. Another possibility might be to restore the first backup to an empty volume, make a snapshot of that, then restore the next backup, and so on until each has been restored and preserved in a snapshot, but that’s far from simple, and laborious.

If you want two or more backups to be maintained by Time Machine, you can always add another volume as a backup store and leave Time Machine to alternate its backups to them, and many users do that routinely.

Controlling backup size

When Time Machine backs up to APFS, there are two separate backups involved: a local snapshot made on each volume being backed up, and the backup itself on your Mac’s backup storage. Local snapshots are normally deleted after 24 hours, but if full automatic backups are made infrequently, they can hang around longer.

You control which folders and volumes get backed up, and which are ignored, using the exclusion list opened by clicking on the Options… button in the Time Machine pane. However, because of the way that snapshots are made, the effect of different exclusions differs on snapshots and backups. Local snapshots are made of all volumes on which anything is to be backed up, and the snapshot includes the whole volume, even those other folders which are excluded.

Let’s say you have an external volume on which just one small but vital folder is backed up by Time Machine. Every hour, Time Machine will make a snapshot of that complete volume and store that on that volume for the next 24 hours. It will also make a proper backup of the contents of that small folder, and store that with the Time Machine backups. If you had a 100 GB temporary file in another folder on that volume, which you’ve added to the exclusion list, that huge file will still be preserved for 24 hours in the local snapshots, even though it won’t appear on your backup storage.

There are two strategies for avoiding unintentionally large backups:

  • Store the large files in a folder which you put in Time Machine’s exclusion list. That will prevent them from taking up space in your backups, but won’t prevent them making local snapshots very large for the next 24 hours, until Time Machine deletes that snapshot automatically.
  • Store the large files in a volume which you put in Time Machine’s exclusion list. As the whole volume is excluded, those files won’t appear in any local snapshots, nor will they be included in your backup storage.

As it’s easy to create special volumes, and they share free space with all the other volumes within the same APFS container, you’ll often find storing such large files on a different volume is a better choice, then both local snapshots and full backups remain small.