rsync vs. rdiff-backup...what's the difference?

What's the difference between rsync and rdiff-backup? They seem to do the exact same thing. My goal is to: Backup changed, added or deleted files on my system from one drive (/dev/hda) to another (/dev/hdb). Actually, deleted files would be removed from my backup upon nightly backup runs. I won't be doing anything over a network. Tom -- Tom Nielsen Neuro Logic Systems 805.389.5435 x18 www.neuro-logic.com