I recently created a file of just over 20GB and then deleted it shortly after, however my free space did not increase at all. I am using a 2012 MacBook Air with a 128GB SSD and I've had problems before with inaccurate free disk space (even when accounting for Time Machine's Local Snapshots). Usually though I can fix the problem by verifying the disk in disk utility, which then shows Invalid volume free block count and orphaned blocks errors, which I could then repair in recovery mode, but now disk utility repeatedly insists the volume is OK, and its S.M.A.R.T. status is verified.

I suppose I will have to just reformat the drive, reinstall OS X and restore from my backups, but is there anything else I can try first? Also, since this has happened a few times before (mainly when I delete a large amount of space in one go), should I suspect the SSD of having problems, in spite of its verified S.M.A.R.T. status?

UPDATE: I initially thought there was a 26.2 GB discrepancy. Interestingly though, whilst System Information reports that backups are taking up 12.65 GB, sudo du -csh /.MobileBackups gives 31 GB. In total, this adds up to 94 GB of used space, which still amounts to a 7 GB discrepancy which I can't account for.


Ok, so after posting this question I had some major breakthroughs, most of which are posted in the update to my question. By then remembering that du still reports in units of 1024 whilst OS X now uses 1000, the final 7 GB was accounted for (well, there's still a potential 500 MB missing judging by Disk Utility, but that's probably just an artefact of du counting in blocks). Now the only question left is why System Information is reporting a substantially lower value for Backups than it should be, and whether or not it will remember to eventually clean up the other 18 GB of local snapshots.

  • And all is now resolved, disabling and reenabling local snapshots cleared the excess. Is this question still useful to anyone now? – nitrous Sep 5 '13 at 12:19
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    More information on enabling and disabling local snapshots can be found here: osxdaily.com/2011/09/28/… – Ɱark Ƭ Sep 5 '13 at 12:42
  • Why not edit the question to be a statement of what you saw and remove the qualifier that it wasn't due to snapshots. You could add a line why you thought it wasn't due to snapshots since other people will likely think the same as you did and perhaps also thing they need to wipe their SSD. – bmike Sep 5 '13 at 13:49

Try using Grand Perspective to see exactly what's on your disk.


  • Interesting, I've tended to use DaisyDisk but I think this will also come in handy in the future. In order to show .MobileBackups, however, you need to run sudo /Applications/GrandPerspective.app/Contents/MacOS/GrandPerspective – nitrous Sep 6 '13 at 13:32

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