So I am trying to clean up my disk a little and ended up looking at the disk utility. Can someone explain this... "thing". It just confuses the hell out of me.

  1. So I have a 256...sorry 250.79GB shared by... what?! 5 volumes ?!!! The left column only shows macOS and macOS - Data under macOS volumes...
  2. Clicking on macOS snapot, it shows the following: enter image description here

The number just don't add up: capacity 250 - available 80 just yield used 170 not 15 !! Also cannot make sense of the graphical bar and its numbers: used 15,41 out of ???? free 67 ?! So available (80 below) is different from free (67)

Seriously, I need help here...


  • diskutil list should help clarify a lot of these issues, since it strictly shows what's on the disk and doesn't show/hide/change things. Here's how that appears on my system imgur.com/a/MAzVww7
    – Ezekiel
    Commented Sep 26, 2022 at 19:03

1 Answer 1


It says 80GB available because 13GB of the data can be purged if necessary. However, it still exists, so it says 67GB is free in the top bar.

15GB is used is the macOS “system” volume. The “other volumes" includes your "macOS – Data", which are your docs/apps. The distinction is made so Apple can block (by default) editing of the macOS volume to secure apps from interfering with macOS (enforced by the signed-system volume and SIP).

The remaining 3 volumes are Preboot, Recovery, and VM. These do specific things and often take up very little space. For example, VM is swap space. It can often be 0B in an idling state. Swap is used when the OS removes data from RAM to the disk so the OS can better use your RAM.

You can list all volumes, without any being hidden, by using the diskutil list command line tool in a shell.

Check out this apple support page for more details.

  • 1
    That Apple article is actually pretty good. This is a nice explanation of a situation that looks normal to skilled eyes, but confusing to someone not read up on the new file system design.
    – bmike
    Commented Sep 26, 2022 at 18:26
  • 1
    I've make a few tweaks to this answer to make sure it's fully accurate - and I've added a few paragraph breaks. Note the distinction between "available" and "free" in the UI
    – Ezekiel
    Commented Sep 26, 2022 at 19:01

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