[Coco] Rainbow on disk RAID

[Melanie and John Mark Mobley]

Key
RoD (Rainbow on Disk)
RADE (Redundant Array of Independent disks)

Error recover of RoD.

RoD RADE => If we had 3 copies of each disk then we could select the sectors
that match 2 out of 3 or 3 out of 3 and recover any errors.
If 2 out of 3 sectors match then use one of the  matching sectors.

Then we can recover from disk errors.  There is hope that we can preserve
this information even if the disk are starting to fail, but we need to act
soon.

John Mark Mobley