I have read the HP 3PAR StoreServ Storage Concepts Guide (http://h20565.www2.hp.com/hpsc/doc/public/display?docId=emr_na-c03606434)
When reading the discussion on page 37-38 about RAID Multi-Parity (essentially RAID 6) the diagram seems odd to me:
The document states:
The following example shows 2 RAID MP sets in one row, the second set is shown below the first set. In the first RAID MP set in the following example, p0 is the parity step for data steps F, L, M, Q, T, V, and X.
V and X are taken from the same chunklet, therefore the same physical disk which seems to break the rules?
Also that is 7 data "steps" and only one parity step, which doesn't seem to be Multi-Parity.
Obviously I am misunderstanding something fundamental here, and my guess is that I am not properly grasping the 2 Sets in one Row.
Do we need to see the two sets as one RAID MP "set", which would see 14 data "steps" and 2 parity "steps".
Also that seems to imply that the parity steps may not be different parity syndromes (X-OR and Galois Field as in traditional RAID 6)?
Can anybody give a good explanation of how a RAID MP works, answer the specific question, or point me to some good resources on 3PAR raid concepts?
There does seem to be a dearth of resources unfortunately. All the resources I have been able to find do not go much further than discussing the basics (chunklets, LDs etc.), and leave the more complex considerations untouched.