[dnanian]

In general, it's a good idea to have some physical redundancy. If your drive isn't a high quality RAID unit (e.g. Infrant ReadyNAS, a WiebeTech TrayDock, the Drobo) then I wouldn't pack too many partitions on it, since if it fails you'll lose all of them, right?

Rotating backups achieves more redundancy because, well, you have more copies of the data across a longer period of time.