Here I have a "fusion" apfs container disk5 made from 2 partitions of physical disks.

  1. I want to add a new /dev/disk6 (/dev/disk6s2) which is a 8TB disk to be used in logical disk disk5.

  2. Then I want to remove disk4s2 from being part of disk5. At the end I should have a disk5 of size 9TB. All this because I want to decommission disk4 transparently for the logical volumes that exist on disk5. --> so I do not want to create a new 9TB apfs container.

How to do that ?

(I did a similar operation recently on a Linux host with LVM and pvmove to move physical extends, and stop using the disk I wanted to decommission, then de registering it from the VG. It was fairly simple).

From Apple diskutil documentation, I can't find out how to do sush operation as 1) and 2).

$diskutil list

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk5         1000.0 GB  disk0s2

/dev/disk4 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.0 TB     disk4
   1:                        EFI EFI                     209.7 MB   disk4s1
   2:                 Apple_APFS Container disk5         4.0 TB     disk4s2

/dev/disk5 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +5.0 TB     disk5
                                 Physical Stores disk4s2, disk0s2

$diskutil apfs list

APFS Containers (2 found)
+-- Container disk5 33333333-3333-3333-3333-333333333333
|   ====================================================
|   APFS Container Reference:     disk5 (Fusion)
|   Size (Capacity Ceiling):      5000572403712 B (5.0 TB)
|   Capacity In Use By Volumes:   3970267238400 B (4.0 TB) (79.4% used)
|   Capacity Not Allocated:       1030305165312 B (1.0 TB) (20.6% free)
|   |
|   +-< Physical Store disk0s2 22222222-2222-2222-2222-222222222222
|   |   -----------------------------------------------------------
|   |   APFS Physical Store Disk:   disk0s2 (Main, "Faster" Disk Use)
|   |   Size:                       999995129856 B (1000.0 GB)
|   |
|   +-< Physical Store disk4s2 11111111-1111-1111-1111-111111111111
|   |   -----------------------------------------------------------
|   |   APFS Physical Store Disk:   disk4s2 (Secondary, Designated Aux Use)
|   |   Size:                       4000577273856 B (4.0 TB)
  • Does this old link help apple.stackexchange.com/questions/226501/… I suspect that you can only 'create' and not 'modify' a Fusion Drive. I hope you have a good backup!
    – Gilby
    Jun 16, 2023 at 0:34
  • I suspect that too but I'd like to find the information to be sure. That would be sad to have so limited tools. Now If I want to swap my HDD for a bigger while still using the same SSD I would have to buy another HDD, and put all my logical volumes on it, then destroy my current apfs container to build a 9TB one, then move back all my partitions back on the new container, then... find a way to recreate the "firmlink" that exist between DATA and SYSTEM type partition of a same os (I have several OSes on my container), then make sure the revovery partition and vm partition still work :-/
    – VinD
    Jun 16, 2023 at 23:36
  • I assume you live dangerously - without a complete backup. Otherwise just wipe the Fusion drive, create a new one, and recover from backup.
    – Gilby
    Jun 17, 2023 at 0:40
  • Well, I do have a backup of my "main OS" where all my important data are. I just have other OSes too (old one,etc...), those are not much customised from a default install but still, they are not backuped and I would prefer not to have to reinstall them. And since I have been able to do that process on LVM I'm really interested to know how it can be done on apfs containers too.
    – VinD
    Jun 17, 2023 at 21:00
  • Don't equate LVM (or other server disk management software) with what is is macOS. Fusion drives are not Apple's equivalent of (or answer to) LVM - so don't expect equal functionality.
    – Gilby
    Jun 17, 2023 at 23:14


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