Preboot taking up 25GB of my disk space

One of my kid’s MacBook Airs has a System taking >50 GB. The solution was to reinstall macOS, using the option to preserve user data.

I did have (and strongly recommend) a backup of the Mac before I did the reinstall, though it wasn’t necessary for that.

When I reinstalled macOS, it was taking ~65 GB (of the 128 GB on her MBAir). After reinstall, it dropped to the ~20 GB that it should need.

BigBlockOCheese wrote:

Hi,

I have a MacBook Pro (M3 Pro) with 512GB of storage.

https://discussions.apple.com/content/attachment/66b2e77f-ba60-4e79-b95f-26f002739796

It annoys me that the system files alone are taking up over 53GB (so over 10%) of my disk space.

OmniDiskSweeper won't show the size of system folders, even with Full Disk Access permission granted, but DaisyDisk showed that 24.5GB of my system folder is taken up by "Preboot".

https://discussions.apple.com/content/attachment/50ce5060-1c6a-4063-91d8-5751c776a47b

From what I've read, most people's Preboot folder is *far* smaller than this, e.g. under 10GB, so I'm unclear why my Preboot is so large, or how to fix this.

As an aside... this query arose due to running low on disk space. I noticed after installing 15.6 that according to Finder, my free space had gone from 30GB up to 120GB (hooray) and research on Reddit showed other people mentioning the same, but at the time I noticed that Disk Utility still reported only 30GB free, contrary to what Finder was telling me. And by the next day, the free space that Finder was reporting had gone back down to 30GB.

For the record, I don't use Time Machine and I have no Time Machine snapshots on my drive (already checked that).

Any suggestions gratefully appreciated!

[Edited by Moderator]

My Preboot volume is 2.5 GB in comparison...macOS 15.6

you can see it from the Terminal.app copy and paste:

diskutil list internal

MacBook-Pro ~ % diskutil list internal

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *1.0 TB disk0

1: EFI EFI 314.6 MB disk0s1

2: Apple_APFS Container disk1 1.0 TB disk0s2

/dev/disk1 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +1.0 TB disk1

Physical Store disk0s2

1: APFS Volume Macintosh HD 11.3 GB disk1s1

2: APFS Snapshot com.apple.os.update-... 11.3 GB disk1s1s1

3: APFS Volume Macintosh HD - Data 564.8 GB disk1s2

4: APFS Volume Preboot 2.5 GB disk1s3

5: APFS Volume Recovery 1.3 GB disk1s4

6: APFS Volume VM 4.3 GB disk1s5

MacBook-Pro ~ %

Also, the user data and settings are preserved, it’s not a ‘fresh system’ in the sense that you’d need to manually restore apps and settings.