Well, unless you symlink index tables to different drives, etc by hand PG currently puts all its files on one drive. This will change in the future, though.
On my own SMP machine I'm just running software RAID 1, on two SCSI drives, with an Adaptec 2840UW controller. I already had a dual processor Supermicro that I got along with a bunch of film from a friend for $100, if I were buying new I'd get a board with the same controller (or the new SCSI160 Adaptec chip) onboard. If I didn't already have a pile of NICs I'd buy a board with integrated DEC Tulip or Intel ethernet, too.
Anyway, if you do want to run a RAID 1 array and do in-machine backups, my configuration (RAID on SCSI, a nice $100 UDMA disk drive for backup) seems reasonable enough. Right now, if you shop you can get IBM's Ultrastar 9.1 GB UW2 7200K RPM drives for about 200, they come with a five year warranty and are perhaps the most reliable drives out there.
RH 6.2's installation program will set up RAID 1 for data disks for you. I put the system on the UDMA drive, at some point I need to replicate it on another UDMA drive so I can come back up quickly if it dies on me, getting RAID 1 up on the root partition's a bit of a pain and I don't mind being down a day if things break.
So, that's my two cents - a couple of moderately priced SCSI drives, a motherboard with onboard SCSI or and Adaptec 2840UW or the latest 160 controller (if Linux supports it already) and software RAID 1.
The 2840 costs about $275 OEM, or did I should say, might be dropping in price now that the SCSI 160 controller's out.
