So earlier today I had a bit of a freak-out! Inexplicably, the remaining 25 GB or so of free disk space on my Mac disappeared. I got a little pop-up warning telling me my disk was full, and sure enough when I checked I only had about 150 MB left. I immediately assumed the worst, that my drive was corrupted, my computer was going to die, all my work would be lost, I would subsequently fail out of my PhD, and that I would end up working at McDonald's. OK, this might be a stretch, and in any case, I have yesterday's Time Machine backup, but I was still freaked out. How do you suddenly lose 25 GB of free space? I noticed it after plugging in my Time Machine disk and letting a backup start. I checked my drive but saw nothing out of the ordinary. On my boyfriend's advice, I let Time Machine finish the backup. This way I could hopefully do a diff between two backups and find out what was eating up the hard disk space.
During the backup, I deleted some small files to help make space and emptied my trash. Then suddenly, viola! My free space came back. My trash had been emptied before, so that was not the cause. Perhaps my Entourage address book had become corrupted? This was one of the files I deleted to help create space since I do not use Entourage at all. My boyfriend thinks perhaps Time Machine itself created some weird temp file that got out of control and that it disappeared as Time Machine finished doing its thing. I do not know what happened, but in the process my boyfriend and I found two great FREE tools that we have now decided everyone should have.
1) Disk Inventory X
This awesome program will show all attached drives, the space used and available, and gives you a really nifty graphical interface so you can immediately see which files are space-hoggers. It takes a little time to get going if you decide to view your entire computer, but trust me, it is worth it!
This utility will list all your Time Machine backups, the space they are using, and a complete breakdown of what has changed since the previous backup.