07-17-2012 09:24 AM
We have 2 new rx2800 i2 with a P410i disk controller and 16 146gb disks in a 2 node OpenVMS cluster. I would like to know the best configuration to provide the best performance/availability to the cluster.
1) Should the disks be configured for RAID5/6 at the controller level and if so, how will OpenVMS see the drives.
2) Should we just use Host Based Volume Shadowing instead of RAID5/6 and create 4 shadowsets.
3) Should we combine RAID5/6 and Host Based Volume Shadowing.
Any help would be greatly appreciated.
07-17-2012 02:32 PM
As I've said many times in the past. RAID 5 was a great idea when disks were 1GB and cost $2K. The price of disk space was high enough to make a reasonable tradeoff of slowing down every write operation in return for some limited redundancy. In the event of a failure, and during recovery, I/O performance goes down the tubes.
Moreover, if you put all your disk (eggs) into a single huge raid set (basket), you effectively expose every I/O to being affected by every other I/O. If you have TWO disk failures you lose everything.
Today, 1GB of disk costs closer to $0.01c, making RAID5 an idea whos use-by date has long since past.
In a VMS Cluster environment, you're much better off in terms of flexibility, performance, availability and recovery to configure everything as host based shadow sets, with dynamic volume expansion enabled. True, you pay for twice as much disk space as you have available, but the cost of disk space is such that it's a very cheap insurance premium. I'd also recommend that for your 16 disks, you keep another 4 on site as cold spares.
Even better, keep some spare hot drives. That gives you more options for moving data around and/or backing it up online (or near online) using 3 member shadow sets.
07-17-2012 11:36 PM
I agree with John that Volume Shadowing is the best solution when you look at flexibility, manageability, etc. The question is whether or not you want to pay for the VOLSHAD licenses.
For good performance I would recommend putting your p410i controllers in RAID mode (mandatory prior to OpenVMS I64 V8.4 UPDATE V0700) and adding the 512MB Cache/Battery kit (HP Part Number AM252A). Maybe you have this kit already because it is mandatory for doing RAID 5/6. It is mandatory as well if you want to create more than two units (with the controller in RAID mode), a "feature" that is nearly nowhere documented.
RAID 5/6 or any other type of units are best created with MC MSA$UTIL. Normally your disks will show up as DKA0:, DKA1,... depending on the unit number specifeid in MSA$UTIL. Do not forget to issue MC SYSMAN IO AUTO after completing the controller configuration in MSA$UTIL.