Non-destructive change to partition size

[BlueMacawBird]

One of my vintage machines (iMac 11,2 Mid 2010) has been set up to run legacy software. It has two partitions, one for Snow Leopard and one for High Sierra. The machine has a 500GB SSD, with the SL partition as Mac OS Extended (Journaled) and the HS partition as APFS. The SL volume is the first one.

I would like to adjust the size of the partitions to shift some free space to HS. Disk Utility (in HS) does not seem to offer a way to do that, and now that I think about it I'm afraid that the different file systems will prevent non-destructive adjustment of the volume sizes.

Is there a way to adjust the partition sizes non-destructively? I would hate to have to rebuild the partitions from scratch.

Thanks,

John

 

[joevt]

You have something like this:

1: SL = HFS+
2: HS = APFS.

You want to shrink SL, then move HS and increase its size.

First you need to boot to a different disk. Or, if you have another Mac, you can connect the iMac to the other Mac using FireWire and boot the iMac into FireWire Target Disk Mode.

Use DiskUtility.app to add a partition to the SL partition "TEMP_PART_A". Set the size of the new partition to the size that you want to give to the APFS partition.

Startup iPartition.app.
https://coriolis-systems.com

Show the Inspector.
Show Pending Operations.
Show Partition Map.
Show Warnings.

You should see something like this in the Partition Map:
1: SL = HFS+ (in the inspector, the "Bootable (reserve 128MB after)" property should appear as selected except for macOS Lion and later which have a Recovery HD instead)
Reserved 262144 blocks (the is the reserved 128MB space that the above property is referring to; macOS Lion and later will have Recovery HD instead)
2: TEMP_PART_A (this is the new partition you created)
Reserved 262144 blocks (it might have this reserved space like the SL partition has)
3: HS = APFS (iPartition.app doesn't know about APFS partitions so the type will be "Unrecognized")

iPartition.app doesn't know how to deal with APFS partitions so don't modify the APFS partition with it.

Inspect the "TEMP_PART_A" partition that you created. Write down the start block number. Delete the "TEMP_PART_A" partition. Inspect the APFS partition. Change the start block to the start block of the deleted "TEMP_PART_A" partition. iPartition should indicate that it will move the APFS partition. Make sure it doesn't also change the size of the partition. Create a new HFS+ partition "TEMP_PART_B" after the APFS partition (as large as possible wherever it will fit).

Note that iPartition prefers blocks (start and size) to be a multiple of 8.

1: SL = HFS+
free space
2: TEMP_PART_A
free space
3: HS = APFS.
4: TEMP_PART_B

Then in DiskUtility.app, you should be able to delete "TEMP_PART_B" which should automatically resize the APFS container?

 

[BlueMacawBird]

Thanks for the suggestion. I'll be sure to back up both partitions before I mess with the disk arrangement, too.