OK -
Some basic math here for those of you arguing SCSI for this type of server -
Let's say he has 300 GB a day - which translates to 300 x 1000 = 300,000 megabytes of transfer a day.
Assuming that you are not having spikes in activity and the server is equally busy throughout the course of the day (not likely but it suffices for now), you are transferring:
12,500 MB/hr
208 MB/min
3.5 MB/sec
That doesn't seem like so much traffic. Yet, these numbers are irrelevant since you will probably have 15x as much activity at some times in the day as in others.
At which point I fail to see why a RAID0 array would not work. If you have the money, RAID 0 + 1 on a modded promise controller would be the best; you would have the redundancy plus the striping.
If your server is of any importance, the mirroring is important, but striping may be able to help you out when you have massive request queues going.
And since these servers are not procsssor dependent, the software-based RAID on the Promise cards would be fine.