Paul Brubaker writes:
Question on Raid 4 vs. Raid DP. We just upgraded to Ontap 6.5.1 and the new feature of Raid DP is now present. Our existing volumes created on Ontap 6.4.2 are setup as Raid 4. Is there any "easy" conversion process to change the old Raid 4 volumes to the newer Raid DP config?
It's very easy indeed. Just go:
vol options [vol_name] raidtype raid_dp
ONTAP will then allocate a spare disk for the extra parity disk and start "reconstructing" it.
Converting back is equally easy:
vol options [vol_name] raidtype raid4
and ONTAP will release the "dparity" disk as a spare.
[That's assuming one RAID group in the volume: each RAID group would acquire/release a dparity disk if there were more.]
Any benefits? Advice? Best practices?
Primary benefit, obviously, is that you are protected against the simultaneous loss of two disks within the same RAID group. (Yes, it does work: I've pulled two disks on a test volume and had it survive!)
Primary disadvantages would be the extra disks (but insofar as it allows for larger RAID groups that may not be an issue) and presumably a not entirely negligible write performance penalty. I haven't had a chance to so any serious measuring of the latter yet.
Chris Thompson Email: cet1@cam.ac.uk