Is the MacPro internal 4 disk raid your boot drive?
I guess you keep all images on the eSata raid external boxes?
Yes, the internal drives are for boot, users and PS scratch disk...everything else is on the external arrays. But the boot drives aren't actually a striped array, it's complicated...You can check out the way I set up the main SAS boot drive and moved my OS X Users folder to the second SAS drive based on this process: Why and How to Move your Users Directory
...it's a bit geeky so I won't explain it here, just look at the web page if interested. The 2 other SAS drives are striped as a RAID 0 for sctratch disk only.