“This disk is used for Time Machine backups”
“OS X cannot be installed on ‘Macintosh HD'”
Those are the error messages I encountered today when I tried to install the new Mavericks OS X on my early 2008 MacBook Pro (it took more than 3 hours to download, but I’ve been having connectivity issues recently).
I found the fix here. It seems you have to look for and delete a folder titled “Backups.backupdb.” It didn’t show up in Finder. I dug around and found it listed with Applications, Library, System, User Guides and Users (under MacBook > Macintosh HD, as I recall) and moved it to Trash, thinking I could restore it from there if the installation still wouldn’t start.
It worked. The installation itself took an hour, maybe an hour and 15 minutes. The countdown timer hangs on “Less than a minute” for perhaps 7 minutes. Just be patient.
For the curious, Mavericks is the name of a surfing location in northern California.