If your extra drive is the same size as your main drive, then you can also setup a RAID, allowing to automatically mirror all data on the main disk.
the exact details will depend on your system's current disk layout, but you can start out by reading some RAID howto's and the mdadm manuals. It's not overly complicated, but it needs some carefull thinking. And you can test data recovery by replacing any of the two disks with a third one.
Last edited by Tinkster; 10-30-2010 at 06:11 PM.