Give your Mac (imaginary) unlimited storage thanks to Disk Utility’s bug

If you could buy a one terabyte external SSD which has unlimited storage capacity, wouldn’t you be prepared to pay over the odds for it? Thanks to Disk Utility in Big Sur, I can now reveal how you can get many terabytes of APFS containers on a single 1 TB disk. The sad thing is that they’re just a figment of Disk Utility’s imagination, a bug, and not real.

Connect your empty external disk, and check that it has a single container with one APFS volume inside it. At this stage, selecting that external disk in the list at the left should show it has a single container and one volume within that. With that disk selected, click on the Erase tool at the top, and format the disk, ideally using the same name as the volume which is already on that disk. You should also get this to work using a different name, although that isn’t anywhere near as amusing or confusing.


If you manage to trigger the bug, you should end up with a 1 TB disk containing two 1 TB containers, as shown above. You can verify that this isn’t a simple container size error using the Terminal commands
diskutil list
diskutil apfs list
which will show the true situation.

Now select the disk again and click the Partition tool above.


You should see something as nonsensical as this: my external 1 TB disk has become, with a little more erasing, 3.5 TB divided into two containers. You can add more containers here, and erase the disk again, preferably using the same name, until your external disk has as much imaginary storage space as you require. Trying to mount its spurious containers results in errors, of course, as they aren’t really there.


I stopped here at 4.5 TB, which I thought was impressive enough.

You should then be able to eject the disk, disconnect it, and a little later reconnect it to see something more closely resembling the sad truth that the disk really does only have 1 TB of storage after all. And that’s your workaround in the event that you stumble into this bug when trying to do something more serious: whenever you manipulate disks or containers in Disk Utility, eject the disk’s contents, disconnect it from your Mac, quit Disk Utility, then reconnect and the disk should be less nonsensical.

I’m hopeful that this bug might at last get fixed before macOS 12 is released later next year (2021).