Are the drives identical? My guess would be yes, but there's no mentions of it there...
Like it was stated, check for a firmware update on the RAID controller, that fixed my problems. Also, if those drives are WD drives, get a copy of the dlgdiag tool on western digital's site to scan the HDs to make sure their SMART table and structures are ok. RAID dislikes defective drives. Make sure your stripped bit isn't too high also (RAID controller tools on bootup, default is usually the sweet spot)
HDTach usually tests RAID well too, try running it to see if you hit the 80/100 meg/sec (If you are in RAID0, of course)