The case of the vanishing disk space

June 01, 2011

This morning I woke up to find an iTunes pop-up telling me that the app couldn't write to the disk because it was full. I thought that was odd because last night when I left the computer I knew there were at least 30GB available on the disk.

SuperDuper! ran early this morning and I have it set to close itself once it's done doing its backup thing. However, it was still open when I hopped on the computer this morning. It had never finished. I looked at the log and it had made it through most most of its routine, but then I saw this at the very bottom, and nothing after it: "04:44:39 AM | Error | ****FAILED****: result=256 errno=22 (Unknown error: 0)."

I had no idea what that error number signified, and so I started digging around my machine. After coming up empty, I deleted about 500MB worth of stuff and rebooted.

When the system came back it still was missing those 30GB. Oddly, it also seemed that whatever disk space was left was shrinking right before my eyes, in real time. I jumped into the terminal and fired up lsof to see if I could nail down the culprit. Nothing. I'm not going to lie, I was kind of freaking out at this point. (Maybe this was VM and I was just more sensitive to it given the situation?)

Then, for whatever reason, I decided to have a quick look in /Volumes, and sure enough there was "backup," "backup 1" and "backup 2." I thought that was odd because I have just two backup drives connected to this machine, "backup" and "backup 2." I unmounted the two drives from within Path Finder, and when I jumped back into the terminal the only mount point that remained was "backup."

I looked at its size and it was clear that this was the beast that had gobbled up my remaining disk space. A quick sudo rm -rf backup and I was back in business.

I'm still not quite sure why the backup volume was duplicated on the source volume (until it ran out of space), but maybe it had something to do with the fact that this was the first backup I attempted since formatting and restoring the source drive from the backup drive? If you've any thoughts, please get in touch.

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