This question has been lurking in my mind for a very long time:
The Wikipedia article for RAID http://en.wikipedia.org/wiki/RAID says that we need 3 disks for RAID4 and 4 disks for RAID6 (NetApp's RAID_DP) array.
But, as per my knowledge, on NetApp's Data ONTAP system, its possible to create RAID4 array with 2 disks and RAID_DP array with 3 disks only.
How is that possible? How does their parity calculations work in this case?