When using Mac OS X you might encounter this message:
The disk "Drobo" is in use and could not be ejected. Try quitting applications and try again.
This message may occur even if you have closed every open program. To force unmount a volume, open Terminal and use the umount command.
sudo umount -f /Volumes/Drobo
Remember to use “sudo” before the umount command.
This will work on any of the mounted volumes on your mac. To view all the volumes, in the Terminal window, type: ls -l /Volumes