mount: disk already mounted or mountpoint busy

If you run into an error message along the lines of mount: /dev/sdb2 already mounted or /media/data1 busy, and the disk has not been mounted, it usually indicates that something has locked it intentionally to prevent it from being mounted. In my case, the culprit was dmraid, a RAID management tool that I am not using any more. Uninstalling the package did the trick. (Removing the array configuration from dmraid would probably have sufficed)

hth.