Jimh,
You're roughly on track, so there isn't much to have at.
Basically there are a variety of RAID levels to choose from, each of which have different performance characteristics, pros/cons and drive requirements.
For large storage servers (like terrabyte+) people usually look to RAID5 as it requires only one extra drive and offers the best cost / performance ratio of any RAID levels.
RAID 5 requires 3 or more drives in the disk array.
Data and parity information are striped at block level across all the drives in an array though. Because parity data is distributed across the whole disk array, there is no single point of failure. (As in RAID4, which nobody uses(?))
Using an arithmetic function (exclusive OR), data on any drive can be computed from parity data stored on the other drives in the array.
Anyway there is a lot of info out there on RAID as more people use it every day. Heck, even Windows now has the ability to do software RAID1 in the operating system. (Started in Windows 2K Server I think)
I've built a number of RAID systems using Redhat Linux though and they run great. Currently I have a 320GB RAID5 system that acts as a file server for all of my MP3's and digital photos. (With a network of Turtle Beach Audiotrons to play music around the house)
Recently I've been looking to re-rip my whole collection to APE and thus need to replace the server with something much larger. Once Maxtor's 320GB models are available in mass (hopefully a month or two
) I should be able to build a nice 1.2 terrabyte RAID5 setup for ~$3500 in rackmount form with redundant power supplies. Install Samba and you have a monster drive to share.