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Eek. I would recommend something that has its own processor and memory on board- like a TRUE RAID controller. Not these cheapo jobs that rely on some software driver to perform the RAID functions and only support 0, 1, or 1/0. Most of those are just cheap IDE controller cards with very basic RAID capability.
You might want to look into a BusLogic, Adaptec or LSI Logic card- there are other major name brands out there too (3Ware etc), but those are 3 of the big ones that offer true RAID cards, good reliability and can be had for not too much cash. Go with SATA if you can- that way you have the capability of talking to all device at the same time. If you get a 2 channel (4 device) IDE RAID card, you can still only talk to 1 device per chain at a time. That's just how IDE works- only one device on a cable can be active at a time. SATA is the same, but you only have one device per cable, so it's not an issue. SCSI can talk to ALL devices at once, but you probably don't want to drop the cash on a serious SCSI RAID.
SATA isn't really any more expensive than parallel IDE these days, so it's worth the investment. I would recommend going with RAID 5 and a true RAID controller. With level 5, you already have your spare. I wouldn't bother with a reserve on top of that, unless you're really worried about losing 2 drives at the same time.