I still go back to look at your set up and can get my head wrapped around what you've written. So how many drives is this in total? How many are in the OS/program dedicated array? Then there's a RAID 0 array of 4 drives in which a mall partition was created for CS Scratch. So where is your data? In the 4 drive array? Doesn't RAID 0 increase the risk of a hD failure losing your data by magnitude of 4? Do you then have some system that backs up your data daily to external drives?
Sorry, let me explain more thoroughly.
1) I have 6 total drives in my Mac Pro. There are 4 main drive slide out bays and the MB has two additional free SATA2 ports on it. So without any added SATA card you can attach another 2 SATA2 drives for 6 total. This device replaces the stock optical bay and allows the two added drives to sit in the lower optical bay while maintaining a single optical drive up top. Note you cannot use this device if you want/need two *internal* optical drives: http://www.maxupgrades.com/istore/index.cf...;Product_ID=158
2) So, now that is cleared up, I have the 2 drives in the lower optical bay in RAID-0 for a 2-drive stripe. These are WD 640G Caviar black drives, very fast dual-platter high density drives with 32MB buffers each, but very affordable for that performance at roughly $75 each. In RAID-0 they act as a very fast 1.25TB OS drive with a huge space reserve for temporary storage of files on the desktop.
3) Now that leaves the 4 drives in the regular drive bays. Here I have 4 WD 640G Caviar Blue drives -- as fast as the black version, but only 16MB buffers and $10 per drive cheaper, so this gives me 2.5 TB of relatively cheap, but screaming fast drive storage. Here I partition off a thin 30G stripe on the fastest outer rim of each drive in the array and use this as dedicated screaming fast 4x30G or 120G RAID-0 scratch drive.
3a) That leaves 600G on each remaining drive. Here I partition off 450G on each drive, so 4x450G for 1.8TB RAID-0 of screaming fast data storage; where I store my working image files and how I get the super read/write performance when working on my images.
3b) The last 150G, or slowest part of each drive is left non-RAID as simple, single drive data storage. Here I use 3 of those for spare bootable copies of my OS. My OS gets cloned over and updated to these 3 partitions a few different times each week, automatically scheduled and run using Carbon Copy Cloner. The last partition is used for Leopard's Time Machine for a different type of back-up and 150G is arguably smallish for that purpose, but the fact is given my particular back-up routine, I don't really need TM at all. Anyway, having these redundant bootable OS partitions allows me to re-boot my machine and re-build my OS instantly in case of a failure on my main OS RAID-0 array per #1.
4) Important: Note that RAID-0 is done for performance only and has reduced reliability over any single drive installation. As such, it is imperative you maintain bootable copies of your OS and redundant copies of all your images as a mandatory practice if you choose to go this route for performance!
5) Note that it takes about 30 minutes total to clone over a full image of my OS including all loaded software, programs and files from any of the slow single partitions, so I can totally rebuild my system in less than an hour AND can keep working the entire time it is rebuilding(!)
6) All of my images are then backed up onsite to a FW800 DROBO, basically an automated 4-drive RAID-5 array for mass storage. This is not a particularly fast device, but it is reliable and has single drive failure protection with the RAID-5 configuration. If the image array goes down, it would take several hours, or basically overnight, to rebuild it reading from a DROBO, but the images (and other data) do remain accessible from the DROBO while that is going on.
7) In case the DROBO fails at the same time as my main box (like in the event of a fire at my studio), I have all my image files further backed up to single bare drives and stored offsite for maximum security.
Makes better sense now I hope?