I figure why bother partitioning. Just create a separate directory for each computer and back up to the directory. Partitions are annoying in that they limit the amount of material you can store on them, so if you decide to put humongous stuff on one computer, suddenly you're rearranging the virtual drives. However, directories are flexible. Anyhoo, that's what I did on my 250gb backup drive, which is FULL and needs a companion. Well, it was full until I dumped all the 2004 Tour de France TV coverage recordings. Really important stuff like downloaded executables, photos, etc., I also back up on CD or DVD.