I maintain a minimum of 3 copies of all my image files:
1. Daily – every night I run a script to synchronize my master working library with a mirrored network backup.
2. Weekly – every week my network backup is automatically synchronized to an additional hard drive.
3. Permanent Archives – periodically I burn DVDs for permanent archival (offsite is ideal).
Once you have the right hardware and software in place, autmating your backups is easy.
I use a Buffalo LinkStation NAS (Network Attached Storage) for my primary backup. I use ChronoSync on the Mac to synchronize my master working library. A second drive is connected to the NAS via USB, and the drive is set up to make updated backups of itself every week.