Just like that: the Finder’s failed trick with APFS

Tommy Cooper (1921-84) was a stage and TV magician who came to specialise in tricks which appeared to fail. In this article, I describe two tricks in macOS Monterey which are worthy of Tommy Cooper’s comic genius, and his nervous catchphrase “just like that”, which he uttered whenever anything didn’t work just like that.

Like all good magicians, to pull this trick off you need special equipment, in the form of an external disk with several bootable copies of macOS installed on it. In my case, I divided it into two APFS containers, one of which has two bootable systems, the other a third:

  • the first container has macOS 11.4 installed on External3, and 11.5.2 on External4;
  • the second container has macOS 12.0.1 installed on External5.

When viewed in Disk Utility in Monterey 12.0.1, this is what I see:


This trick starts by connecting that external disk and waiting until all its volumes have mounted in the Finder, adding External3, External4 and External5 to the list in Locations. Then I simply click on the eject icon ⏏ next to External5. The Finder then asks me to clarify whether I want to eject just that volume, or all three of the volumes on that external disk.


I next click on the blue Eject button, so that it will just eject External5 just like that, as Tommy Cooper would have said.


That brings laughter from the audience, because the Finder promptly ejects all three volumes. But it isn’t as simple an error as that. Looking in Disk Utility, the External5 volume group (System and Data) are now unmounted, as are both Data volumes in the other container, External3 – Data and External4 – Data, but their System volumes are still mounted.

Had I used the Eject All button in the previous dialog, all three volume groups would have been unmounted as expected.

With a little nervous laughter, I then explain that I’d better use Disk Utility instead, so quickly remount all the volumes again, and demonstrate that does work correctly. That is, so long as I don’t try unmounting a volume group or container in Disk Utility. Although it’s not such a reliable trick, that normally only unmounts the System volume, leaving the Data volume still mounted.


At this stage Tommy Cooper would look puzzled and anxious, emit another nervous laugh, and push the Mac to one side ready for another trick. I’m hoping Apple’s engineers might stick with these bugs until they’re fixed.

I’m very grateful to Thomas Tempelmann, who drew my attention to this little piece of failed magic.