hmm..well i would think thats what a mirror raid setups for. But i dont think its possible to ghost the array, as both hds would need to read simultaneously. Otherwise u'd probably need like 4 hds and back up each seperately..
RAID Mirroring (That's RAID-1 I think . . . But it might be RAID-5) is a form of RAID Redundancy. It takes everything on drive 1, and copies it to drive 2, so if drive 1 dies, you can backup from drive 2.
Um . . . I don't mean to nit-pick, but you're a little wrong on that. RAID5 backs up a bit of each other drive on all 3 drives. So if drive 1 dies, it could be rebuilt w/ drives 2 and 3. I'm pretty sure that's how it works.