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I've got an external hard drive ("HDD A") formatted HFS+, which is backed up to a Time Machine drive also formatted HFS+. I'm going to replace HDD A with another external hard drive, formatted APFS - I'm planning to copy the contents of HDD A and transfer it to the APFS drive (using Carbon Copy Cloner).

Is it possible for Time Machine to continue with the HDD A backups on the APFS drive (ie. so that the next backup is incremental, and it's easy to browse backups in Time Machine.app), even though a filesystem change has occured?

It seems like I should use tmutil associatedisk (but thought I would check, since I don't want cause a problem with my Time Machine backup history).

(In case it's relevant, I'm using macOS Ventura 13.0 (so the -a option for tmutil associatedisk isn't available)).

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    Not possible. Never easy to copy TM backups and impossible between TMhfs and TMapfs. Just keep the old drive and, when/if needed, plug it in and use Finder to recover files. Create new apfs volume on new HDD, tell TM to use it, and TM will erase the volume and start new clean backup.
    – Gilby
    Nov 8, 2022 at 5:20
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    @Gilby Sorry, I meant - if TMhfs is backing up another external hard drive in HFS+, and that drive is replaced with an APFS drive with the same contents, could the backups continue? I'll update the post to try to make it more clear.
    – Cloud122
    Nov 9, 2022 at 3:55
  • Got it. Your position is exactly as the scenario in man tmutil under assocaitedisk and which you have obviously read. Sadly I don't know enough to encourage you to risk the experiment!! Let's see if someone else comments or has a robust answer.
    – Gilby
    Nov 9, 2022 at 5:40

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So Time Machine backups can continue from an HFS+ external drive to an APFS drive, using tmutil associatedisk. (I ran the script from here, since the -a option isn't available in macOS Ventura.)

for f in /Volumes/Backup/Backups.backupdb/James\'\ iMac/*; do
   if [[ -d "$f" ]]; then
      sudo tmutil associatedisk /Volumes/HDD\ A "$f"/HDD\ A;
   fi;
done

After running the script (there was no output that it was successful), the next backup for HDD A was incremental, and the full backup history shows for HDD A in Time Machine.app.

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