Will using Virtual Replicator improve performance

[andy steven]

Hi

Have a msa 1500 with 4 SB shelves.

to provide redundancy to a shelf failure i was considering using 1 disk in each shelf and creating a RAID 5 sorage unit. creating about 4-5 of these and then adding them to a pool and presenting this out as a virtual disk. Will i gain performance in doing this, is each storage unit viewed as a disk with multiple spindels??

sorry if not explained very well

[Steven Clementi]

Andy:

You thinking sounds solid to me. I would consider doing this in certain situations. I know I would not want a shelf failure to hose all my data.

Here are a few comments and tips:

1. You will effectively be using all the spindles just as if you configured a 16 to 20 disk Array. Will you gain performance? If so, it can't be much more than if you just created the large array with ACU. It might even be less since now on top of the controllers having to do work, you now have VR which needs to do work, taking cycles of CPU on your host.

2. VR gives you the ability to hot add/remove/extend storage as requirements change.

3. If you do not need the Shapshot functionality, you can reduce the default values so that it does not eat away at your available storage. The default vaule VR "holds" for snapshotting is 30%. I have reduced this to as low as 5% in the past and can probably go even lower. Let me know if/when you want to do this and I will give you the details.

4. You need to present RAW storage to VR. Do not write a windows disk signature to the disk. only check in Disk Management to make sure the system can "see" the disk.


Steven

[andy steven]

Thanks for the advice.

VR does seem to offer some nice features, however i really don't like adding another layer of software into the mix (just another thing to go wrong).

Hp states that VR's snapshots are quicker than MS, do you know if this is correct.


I will do some tests, just thinking about doing a server recovery with VR is making my head hurt..

[Steven Clementi]

When you say MS, I assume you mean MS's Volume Shadow Copy service as I never heard of another "snapshot" service from MS.

If so, then the 2 concepts are slightly different then what your probably thinking.

A Snapshot, for all intense purposes, is just a point in time mapping of the original data. What this means is, the snapshop is not an actual copy so it happens VERY quickly... a few seceonds even. How the snapshot works is as follows...

There is Data in Container 1: Data A and Data B

The snap shot is taken and a map is made ,"pointers" to the original data. This would be Container 2.

Container 1 is changed, now "Data C" is added. The snap shot has no changes because Data A and B have not changed.

Container 1 is changed again, now Data B has become Data D. Before Data D is written, Data B is written to the snapshot space. Now the Snapshot still has it's pointers back to Data A, but also holds Data B since the original location was overwritten

Container 1 holds Data A, Data c and Data D
Container 2 holds Data B and Pointers to Data A.

MS's VSC makes actual copies of data periodicly as it changes during the day. It is similar in ways such as it holds old data for a pre-defined period of time, but I think it operates a bit differently then traditional HP Snapshot'ing.


Steven