The Mystery of Disappearing Disk Space

Very new to the forum, appreciate any help.

I know this topic (or variants of) have been posted in the support community, some going back quite a ways but I have yet to find an answer. Maybe I have not looked in the right place.

To start, I have a 15” MBP, mid-2009, 500GB HD, 3.06 Ghz Core 2 Duo, 4 GB 1067 MHz DDR3, running Mt Lion 10.8. I am using Time Machine to back up, one disk on the desktop connected to MBP and the other comes out every 2 or 3 weeks, then back into a fire proof safe.

Background: last week, I got Apple TV and subscribed to iTunes Match, thinking I could recapture some HD space by removing 4 seasons of Fringe and about 20 movies as I am making more room for 1000’s of photos to be edited in Photoshop CS6 and Aperture.

I deleted the iTunes files above; only to find out that the available HD space had gone down from 139GB to 132GB. Not the right direction. I should have easily recovered 130GB to 150GB at least.

1^st trip to the Apple Genius Bar, I was told everything checked out fine. The volume was verified via disk utility, and after poking around for sometime he said that perhaps “About This Mac” “Storage” tab was reporting faulty data and that I needed to reinstall MT Lion. If that did not work I was to “erase” my HD and perform a “recover” from Time Machine. For me, this was pretty drastic but went home and reinstalled MT Lion. This did not solve the issue so I stopped.

After searching this forum, I discovered, downloaded and ran, Disk Inventory (DIX). It revealed that I had over 150GB in the infamous “folders occupied by other files and folders”, all, which I could not find on the HD. Further searches online, revealed possible causes could be related to “sparse tables”, “time-machines local snapshots”, etc. At this point, it is over my head and went back to a different Genius Bar (we have two in St. Louis) for another opinion.

While he was poking around my system, I told him, one thing was also ways odd to me after moving from SL to Lion and MT Lion, was that in both Lion and MT Lion, whenever I deleted a file, a window always popped up asking for my password to trash any file. I would enter the password and the file was immediately trashed. Trash can was empty. Per that discussion, he then verified disk permissions (which revealed issues) via the recovery disk in Mt Lion and also turned on the hidden files. After a while, he discovered some type of trash file was holding the ~150GB. He deleted it, made some other changes via terminal, restarted and viola, all the disk space was back. The trash now work properly on the desk top, in that when I delete something it goes to the trash-can and if I erase deleted items in the trash can, it empties, or so it appears.

The problem is that after I returned home and did some further trimming of Aperture projects, the symptoms are back. After running DIX, “folders occupied by other files and folders” now continues to grow anytime I trash some files, even though the desktop trash can is empty.

The guy at the genius bar seemed to find (and delete) the offending file/s but not necessarily the cause. I am hoping that someone really familiar with how MT Lion operates can shed some light onto this. Sure, I can keep going back to the Genius Bar when I need more disk space and they can dig into the terminal and delete these files, but why is it happening and what is the solution.

Thank in advance,