Solving Time Machine’s “Case-Sensitive” Problem

Guess who wasted most of their morning trying to get Time Machine to backup their Mac. Still, with this blogging lark it’s never really time wasted — I can always make a post out of the experience. So here goes. For the benefit of Google, the error message in the screen grab above reads:

A volume you are backing up is case-sensitive, but the backup volume is not.

To select a different backup volume, or to choose not to back up the case-sensitive volume, open System Preferences and choose Time Machine.

This happened when I plugged in an external FireWire drive which had worked just fine the last time I’d backed up, about a week ago. (Yeah, I know, bad me.) In the intervening days I hadn’t installed any new software, let alone changed the format of my single main drive. Sure enough, a quick check showed that both main and backup drive were standard ‘Mac OS Extended (Journaled)’ volumes. And Mac OS Extended — aka HFS+ — is not case-sensitive by default. Restarting the Mac didn’t help. I fired up Disk Utility and verified both drives, but that yielded no errors, either. Curious.

It was while glaring at my MacBook Pro’s screen that I notices listed in Disk Utility’s side bar the disk image I’ve used in the past when playing around with the DarwinBuild environment. (Believe me, if you don’t know what that is you really don’t want to know.) Now that was a case-sensitive UFS volume. But it wasn’t mounted: it didn’t show up in the Finder, nor under /Volumes in the Terminal. On a whim, and for want of something better to do, I removed it anyway and restarted. Time Machine ran without complaint. So there’s your solution: check to see if Disk Utility is remembering any disk images it shouldn’t be.