How to set up Time Machine to use an internal disk

I want to use some of the features of Time Machine but don't need or want it to be backed up to an external drive.

However, Time Machine doesn't show internal disk's when selecting a drive to use. I have even created a separate partition but it still doesn't see it.

How can I get Time Machine to back up to an internal drive or partition on the same hard drive?

MacOS 12.1 Monterey / MacBook Pro (16-inch, 2021)

Solution 1:

The main purpose of Time Machine (indeed, of any backup software) is that if your internal drive fails, or your device is lost, stolen or broken, you still have another copy of all your files on a separate device.

A copy on a partition of the same internal device provides no such safety net, which would explain why it won't let you do it.

Depending on what features you actually want (I hesitate to say 'need' without knowing whether you do actually have a proper backup strategy), you will have to use another sync/backup software.

For instance, if you only want versioning, then this capability already exists within the APFS format, in the form of snapshots.

If there is some other reason why you want to use TM, I'd still recommend making a backup to an external drive, as you can never have too many backups.

(Also, given that the internal SSD is part of the system-on-a-chip and not replaceable, duplicating every write with another copy may be incautious.)