RAID = Redundant Array of Inexpensive Disks. You've heard us talk about it on the show. To most people ihttp://www.bjorn3d.com/read.php?cID=886t's black magic, despite it being fairly easy to do (in some types of arrays) and a very good solution for safekeeping of your data.
If you want to know about RAID; what it is and how to use it, I suggest you click on the link above and follow along as this multi-part article is published. The link takes you to Part 1.
With hard drives as cheap as they are, mirroring one's primary drive is a good way to ensure that if your main drive goes kaput, you can merely rearrange them and boot from the mirror drive. It's virtually as simple as that sounds, too. You probably need to check this out if you're not already up to speed on RAID.