I have a tale of woe to add here.
I recently bought a new PC based on the ASUS A7V8X motherboard, which has onboard RAID. It's one of the kind that needs an OS driver. I ordered it with a 40G drive with WinXP installed on it. I bought two Serial ATA 80G drives to create a RAID-0 (striped) array. The FastBuild configuration went well; it detected the two drives and I told it to stripe them. The OS already had the RAID drivers installed so it recognized the drives as one 160G drive and I was able to add partitions to it with PartitionMagic (a great program, by the way). BTW, Master/Slave doesn't apply to SATA, every drive is on its own cable.
I decided to install a copy of WinXP on the striped drive, with hopes of increased performance dancing in my head. I copied the RAID drivers to a floppy and hit F6 during setup when it asked if I had drivers to install. Worked like a charm, I was able to install the OS on the striped drive, it showed up in my boot menu.
HOWEVER: It doesn't seem to work! When booted to the striped drive I get daily crashes and other mysterious lockups that don't respond to ctrl-alt-del; I have to power off the system to get out of it. It doesn't happen when I'm booted to the non-striped OS.
Moral of the story: Keep the OS installation you have and install a second copy of the OS on the striped drive. (I always have at least two OSes installed on two separate drives.) Maybe it will work for you.
Me, I'm going to look for a 100% hardware RAID solution that presents the striped disks to the OS as one disk, without the need for potentially buggy OS drivers.
Mike Persons