Right now I'm running a 3 disk Raid0 (500GB per) for my storage and an Intel 40GB SSD as my boot/windows drive it will soon be a 4 disk Raid0 (500GB per) and a Raid0 with two 40GB SSDs (obviously, I just care about speed and not data security, that's what backup is for ) - I also tried the 3 500s in a Raid5 and for some reason it was just horribly slow on the writes. Like, copy a directory and it was 25MB/s... whatever. Anyways, I ran HDTune (yaya) and I must say that the current Raid0 blew me away with the transfer rates etc, and the SSD could not be touched for random access - in fact, I have a 1TB Samsung as a backup drive and it only did 1MB/s less on random access than my Raid. Gotta love those SSDs.
However, I am on the fence if I should go Raid1+0, Raid0 or Raid5 when I get the 4th drive - a little bit of "security" is always nice to have I am however totally sure I will do the Raid0 on the SSDs (mainly for more storage on the boot drive)
Do the raid 0 if you plan on continuing the backups 0+1 if not I had a raid 0 with 5 disks and it was smoking lost a drive and then reformated as a 4 disk raid 0 it was just blazing fast on map loads and program opening nothing like the ssd that replaced it but my 5 disk raid 0 was faster transfer rate than my ssd just no where close in access time. SSD for the win but I loved my pile of raid while I had it. Raid 5 writes are slow as it has to calculate parity for every write and since there is no hardware to do this it has to use the processor this slows it down a bit.
I also tried the 3 500s in a Raid5 and for some reason it was just horribly slow on the writes. Like, copy a directory and it was 25MB/s... whatever.
RAID-5 has by far the worst write performance of any RAID organization. It's not because it has to calculate the parity (the actual work to XOR the data to generate the parity sector is trivial) but because it has to update the parity on the drives. For each sector that you write, a RAID-5 set has to first READ the old parity, then use it to calculate the new parity, and then finally WRITE the new parity and WRITE the new data. It's those extra read/write operations that kill the performance.
Raiding drives for performance kinda defeats the purpose of redundancy. But if you ask me, you'll get far superior performance from simply upgrading to a larger SSD. Those 40GB drives even raided are no match for most of the 120GB drives out now. 240GB seems to be the sweet spot for ultimate performance, but that comes at a price premium.
I'd invest in a 120GB drive, I came from a 40GB Intel drive and it was a vast improvement. I'm running the 120GB Vertex III, and I love it. The m4 drives are also very nice.