If a drive fails, replace it and the array will rebuild using the new drive
The array will operate minus one drive, but about 25% slower.
RAID 5 on Intel works like this:
If a drive fails, replace it and you have to wipe out the array, rebuild all 4 drives, and restore from your backup (which you don't have because you should not need one with RAID 5)
So I replaced what was marked as a failed drive, and could not access anything on the array. I put the bad drive back in, and at least now I can run on 3 drives till I can make a backup. So I'm off to Fry's or Microcenter to get an external drive to back up to. The I guess I'll re-do the array as RAID 10, which will give me the ability to do the drive swap thing, but at the cost of 500GB of usable space. Argh. and Harumph.
I am sooooo glad I put the OS on a separate drive.