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My computer is a late 2011 MacBookPro with an original 128 SSD running MacOs 10.13.6. For some years now the total of the used disk space plus the available disk space has been slowly shrinking. In particular, the available space keeps (slowly) decreasing, even if I do not use additional storage space.

Right now the free space is 11.5 GB out of a total capacity of 128 GB. Looking at "About This Mac > Storage" I see the following ("Documents" is 31.77 GB, blue is "Apps" with 6.69 GB, dashed is "Other Volumes in Container" with 3.88 GB)

System information

Using OmniDiskSweeper v1.11 I get this instead

OmniDiskSweeper v1.11

that sums up to roughly 67 GB used in total.

My question is: what is eating up disk space behind the curtains? Is this a software related problem or an hardware related problem? (since my SSD is one decade old, is there some mechanism that marks SSD sectors as unavailable when they break or become unreliable?)

Additional information:

  • Time machine is enabled, I did the latest backup yesterday on an external hard disk, but available space did not change, even after a restart.
  • About three months ago I made an accurate clean up of my hard disk using "Clean my Mac" to detect junk and manually deleted the actually useless files (caches, old files, unused apps, ...) reaching 25 GB of free space. Yet, after a few months, space slowly shrank to 11.5 GB.
  • I found lots of other similar questions here and on the internet, but no answer seems to make sense in my case.

UPDATE (22/12/2022)

I scanned my ssd using Daisy Disk and got the following result. Any suggestions on how to get rid of those 41 GB of hidden space? (Daisy diary requires to buy the full version to display further details and I would like to avoid it).

enter image description here enter image description here

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  • Do you keep adding music, photos, files etc?
    – Solar Mike
    Commented Dec 22, 2022 at 9:48
  • No, nothing like that. As you can see, there is a huge difference between the report provided by System Information and the one provided by OmniDiskSweeper. The issue might be less trivial than that.
    – Sirion
    Commented Dec 22, 2022 at 10:34
  • For 3rd party apps, I strongly recommend Daisy Disk as well, which does have a free trial.
    – Ezekiel
    Commented Dec 22, 2022 at 14:55
  • You mention Time Machine, which will enable a feature called Local Snapshots. However, these local snapshots shouldn't be persisted more than a day or two which means it shouldn't display what you're seeing here. However, you can try tmutil listlocalsnapshots / in terminal. Check the age of the snapshots to see if any are hanging around.
    – Ezekiel
    Commented Dec 22, 2022 at 14:56
  • Apparently everything is fine: $ tmutil listlocalsnapshots / com.apple.TimeMachine.2022-10-13-220203 (dataless) com.apple.TimeMachine.2022-12-22-175223
    – Sirion
    Commented Dec 22, 2022 at 17:29

1 Answer 1

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Long story short: at some point I booted my mac keeping the D key pressd to start the Apple Diagnostics utility, which revealed this error: 4HDD/11/40000000: SATA(0, 0).

According to the internet, this should mean that I have an issue with the cable connecting my ssd to the motherboard (but according to others it may also be a false positive...).

Anyway, I opened my macbook pro and found a small piece of dust stuck under the connector of the ssd cable on the motherboard. After removing it Apple Diagnostics utility did not report any problem.

However, I have not been able to fix the corrupted filesystem using fsck_apfs in any boot mode (safe mode, single user mode or recovery mode), hence I decided to make a clean install of MacOS 10.13.6 after manually erasing the whole disk using Disk Utility in recovery mode.

It worked! I have been using my "new" macbook pro for a couple of days with a predictable behaviour of the available space and fsck_apfs says that my filesystem is clean.

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