Shoud we apply stripe volume on Hardware Raid

[pgm10s]

I wonder about the benefit of create the stripe volume usig SF on the LUNs of Hardware Array. 

[mikebounds]

You can get improved I/O by VM striping on top of LUNs which are striped at H/W but you have to make sure the columns in stripe set in VM come from different RAID sets on the array and you may only see an improvement when you exhaust the cache on the array (i.e if you are doing a lot of writes like importing a database)  

I think it also depends on whether you are doing serial or parallel writes as I think if you do serial writes to a VM striped LUN, then VM effectively splits those writes across the LUNs in the stripe set and so parallelises the writtes which I belive improves I/O.

I have heard a lot of SAN guys says it makes no difference, but I had a collegue who did some tests which was about 10 years ago and there were improvements, but there was a limit to the improvement so once you got past about 4 LUNs you see little improvement and with about 6-8 or more columns, I/O can start getting worse.  As this was 10 years, array technolgy changes may mean the results are different, so if you really need to push I/O, then best to do some testing on different column (and stripe width) writes to see which gives the best results.  

Mike

[pgm10s]

We use IBM v7000 in the systems. The LUN is made from all physical disks in the POOL.

So the stripe shoud not improve the performance.?

[mikebounds · Accepted solution]

If all disks are in one pool, then I think it is unlikely that striping across LUNs in that single pool would give any improvement in performance and may even make it worse than a non-striped volume.

Mike