Resizing a partition in Mojave

[wmtbt (William M.)]

I have a backup drive (presently formatted as HFS+) that is 2 TB total and partitioned into two 1 TB partitions. However, my internal drive is only 256 GB, so I would like to resize the first partition on the backup drive to be 256 GB, giving the rest of the space to the second partition. I know I could reformat it and just redo my backup, but I should also be able to resize it non-destructively, right?

I went into Disk Utility, but couldn’t figure it out.

Thanks!

[mpainesyd (Michael Paine)]

I haven’t done this myself but try holding the Command button down when you have the partition map displayed in Disk Utility. It might display the resize handles (a tip from an old Apple Discussion).

[j.albert]

There used to be (still is, read on) an app by Coriolis named “iPartition” that could do this for you.

With the coming of APFS, Coriolis generously made its apps “iPartition” and “iDefrag” FREE and available from their “software museum”. You can find that here:

Coriolis Systems

Please note that the museum contains various versions of each app.
You may have to download and try more than one until you find which version works.

I have an m4 Mini with Sequoia installed, and iPartition 3.6.2 opens for me.
Here is what it looks like, opened and viewing my m4’s internal SSD:
(note that the system container is APFS [and “unviewable”], but the other working partitions are HFS+)

[Shamino (David C.)]

Disk Utility is limited.

From its manual:

Enlarge a partition on a storage device

If you have multiple partitions on a device and one of them is running out of space, you may be able to enlarge it without losing any of the files on it.

To enlarge a volume, you must delete the volume that comes after it on the device, then move the end point of the volume you want to enlarge into the freed space. You can’t enlarge the last volume on a device.

So, you should be able to shrink the first partition without any problem, but you won’t be able to move the second partition to fill the space.

If there is less than 768 GB used in the second partition, then you can (probably) do this:

• Shrink the first 1TB partition to 256 GB. The result will be:

  0 .. 256 GB: P1 1 (256 GB)
  256 GB .. 1 TB: Free space (768 GB)
  1TB .. 2 TB: P2 (1 TB)

• Create a new partition in that middle free space:

  0 .. 256 GB: P1 (256 GB)
  256 GB .. 1 TB: P2new (768 GB)
  1TB .. 2 TB: P2 (1 TB)

• Use your favorite tool to clone P2 to P2new

• Delete partition P2

• Use Disk Utility to grow P2new to fill the rest of the drive

• Rename P2new to P2

If there is more than 768 GB in P2, then you might (not sure) be able to do the same thing in multiple steps, creating and deleting temporary partitions as needed. But I’m going to leave this as an exercise for the reader. It will probably be easier to just buy a new drive and backup/delete/create/restore the P2 partition.

See also:

Partition a physical disk in Disk Utility on Mac

[wmtbt (William M.)]

Thank you to all who responded. I am fortunate in that the second partition on the drive was completely empty. Thanks to your answers, I was able to remove the second partition, shrink the first to 256 GB, and then add the (now larger) second partition back.