VSA Raid Reconfiguration

Steve Irvine — Thu, 10 Jun 2010 15:35:33 GMT

Hello,

I have 2 VSA's on HP DL180s using 8 x 1TB disks.

I chose raid 5 using 7 of the 8 disks, leaving one as a hot spare, then carved it up into <2TB luns and presented those to the VSA.

Am I right in assuming that the VSA has now performed a software raid-0 on those luns?

If so I have a feeling that I may have royally shafted performance. Since the VSA's raid 0 is at 90 degrees to the original raid (if you see what I mean). It seems like I might have made continuous reads very difficult.

Since I chose a 7 disk raid 5 usable space ended up being approximately 4.5 tb.

I wonder if I might be better making 4 raid 1 sets on the dl180 then presenting those to the VSA instead. If the VSA is going to do a software raid 0 whatever I do then this should be a far better configuration.

My question is, if I break the VSA cluster and reconfigure 1 node as a smaller unit, will I be able to re-introduce it to the cluster?

I am only using about 1TB of space right now so if when I add the new node the cluster just configures down to the new size that will be fine.

However if a VSA will not add itself to a cluster when it's smaller than the current node size then I am in trouble. Or at least will not be able to reconfigure without downtime.

Re: VSA Raid Reconfiguration

douglas carson_1 — Thu, 10 Jun 2010 20:13:25 GMT

You will not be able to introduce a smaller VSA into your current cluster. imagine it like disks in a RAID set.
The VSA doesnt have a RAID configuration, it uses the underlying RAID configuration of the disks on the ESX host.
One thing to note is if you use a large RAID 5 with SATA disks it is advisable to look at RAID 6. Due to the size of the disks it can take a long time to rebuild the array if there is a disk failure. During this time the likely hood of a disk is higher, due to the array having to deal with production I/O, as well as the rebuild. Maybe something to keep in mind.
Hope this helps
DC

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