I have an eight-terabyte powered drive formatted as follows:

/dev/disk12 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *8.0 TB     disk12
   1:                        EFI EFI                     209.7 MB   disk12s1
   2:                  Apple_HFS Seagate 3TB             3.0 TB     disk12s2
                    (free space)                         134.2 MB   -
   3:                 Apple_APFS Container disk13        5.0 TB     disk12s3

/dev/disk13 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +5.0 TB     disk13
                                 Physical Store disk12s3
   1:                APFS Volume Seagate 5TB             4.0 TB     disk13s2

“Seagate 5TB” is a Time Machine backup drive.  “Seagate 3TB” is empty except for .DS_Store,.Spotlight-V100, & .fseventsd which are meaningless on an otherwise empty volume.

If possible, how can I convert it into a single APFS volume with one container and two volumes, merging 3TB and the free space into one volume, with 5TB the other volume, without breaking the backups already in 5TB?

If necessary (and possible), I could copy the backup set to an empty 5TB physical drive and copy it back.  But I’d rather not, because that would take a LONG time (5TB is already 4TB used).

I think I would also need to set quotas, to change 8TB to 6 TB or less and 3TB to 2 TB or less (renaming both).

I do not trust the AI-generated answer that tells me to backup the backup and then erase. :-)

  • Your AI answer will preserve data on the 3TB, but zap the 5TB.
    – Gilby
    Commented Mar 16 at 5:28
  • AI stands for “Artificial Idiocy”. (It seems these AIs are programmed never to give you no answer. I would have answered “not a clue” but the AI want allowed to. )
    – gnasher729
    Commented Mar 16 at 7:53


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