I stopped relying long ago on RAID-5 after I had two separate installs that the controller card corrupted more than one disk in the array at the same time, causing total data loss.
When you're dealing with more than a terabyte of data, restoring from any sort of backup medium becomes a painful process. All of my data is backed up on DVD (yeah yeah, I've heard the complaints before, but you don't know what I know about DVD backups) but restoring a terabyte of data from DVD's can take a week or so.
Enter DRBD. DRBD stands for Distributed Block Device. Essentially it's RAID-1 that works over Ethernet. DRBD rides on top of whatever physical storage medium and network you have, but below the file system level. You run it on multiple machines, and set up an identical hard drive configuration on each machine. The DRBD partition is automatically replicated from the primary server to the secondary. Using tools like "heartbeat" you can even monitor this system automatically and promote the secondary server to the primary in the event of a failure.