Partitions with different formats?


iMac (Retina 4K, 21.5-inch, Late 2015)
Booting from external Samsung T5 using latest Monterey

I’m sure many here can answer this but I couldn’t find an answer doing a web search.

I have an external 4 TB HD split into a 3 TB partition used for TM backups and a 1 TB partition used for SuperDuper backups of my system. Both are formatted as Mac OS Extended (Journaled).

I am booting from the external T5 and creating ‘bootable’ backups to the internal Fusion drive, both APFS as required.

I was maintaining an older OS on the 1 TB partition to fall back on while I experimented with Big Sur and now Monterey, but now I’d like to use it as another up to date Monterey backup. This means it will have to be reformatted as APFS.

In the long term I suppose I’ll have to move TM backups to APFS, but I don’t want to lose the 2.5 TB of TM backups that are currently on the Mac OS Extended volume.

My question is can I reformat one partition on the HD without affecting the other?

Thanks for any and all thoughts.

Disk Utility should let you resize partitions.

So if all you want to do is use the remaining 1TB for additional TM storage, you should be able to delete the 1TB volume and then resize the TM volume.

If you actually want to migrate to APFS for TM, then you can (I think):

  • Turn off TM
  • Delete the 1TB volume
  • Resize the 3TB volume to make it smaller (so you’ll have additional APFS storage)
  • Create an APFS container in the free space
  • Create an APFS volume in the container
  • Reconfigure TM to use the new APFS volume instead of the existing HFS+ volume
  • Turn TM back on

You’ll have the old TM volume for accessing historic revisions, while new backups will go to the new TM volume.

In the future, when you decide you no longer need the old backups, you can delete that volume and expand the APFS container to fill the entire device.

Or, since hard drives are pretty cheap, you may want to just retire that device and get a new one for a TM-over-APFS volume.

Thanks for your thoughts. I guess I didn’t express myself clearly. I want to use the 1 TB partition for SuperDuper backups of my Monterey system. It would have to be reformatted as APFS to do that. Will reformatting that partition have any affect on the 3 TB partition that I want to leave as HFS+ for TM backups? Or, to put it another way, is it okay to have partitions on a single HD formatted using different formats?


Jack Clay

Sorry for the misunderstanding.

No, you shouldn’t have to do that. Delete the HFS+ partition and replace it with an APFS container. Then create an APFS volume in that container.

When you make your clone, if you are making a bootable clone (of questionable utility these days, especially if the destination is a hard drive), then the clone process should create additional volumes within that APFS container. But it shouldn’t touch the HFS+ volume, which is in a separate partition.

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