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Stripe size

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July 14, 2009 5:13:30 PM

here are the particulars:
raid card: Adaptec 5400 series
drives: Western Digital WD5000ABYS R3
amount of drives: 14
raid set: raid 5 with hot spare
enclosure: SuperMicro 836E1
O/S: windows storage server R2
What would be the recommended strip size and why... currently we use the manufacture default setting, 256k, we do this because some of the raid is provisioned via ISCSI and used for VMware. We have been told that due to the combination of ISCSI and VMware the larger size would be the best answer... we would like some other input though.
regards
Paul

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a b G Storage
July 15, 2009 11:17:27 AM

Based on experience; file size contributes about 20% while 'optimal/preferred' contributes 80%. The modern hardware RAID controllers of today usually work best between 128KB to 512KB. In rare cases like putting OS+app on RAID0 or 10 then 64KB seems to work well.

The particular controller I'm using, a Dell PERC 5/i (flashed to MegaRAID SAS 8480E) performs best with a stripe size of either 128KB or 256KB. I'm using 256KB with a 4x1TB RAID5 array.
July 15, 2009 1:17:25 PM

I thought that a larger size would be best. thanks all
Paul
a c 127 G Storage
July 15, 2009 4:20:36 PM

If your windows has bad partition offsets, a larget stripesize may help prevent misalignment. For example with Windows XP default install:

128KiB stripesize: always misaligned (100%)
256KiB stripesize: mostly misaligned (50%)
512KiB stripesize: 25%
1024KiB stripesize: 12.5%

This shouldn't be an issue with Vista and Win7, as they align partitions properly, im not sure about the server versions. Aside from this, normally a higher stripesize wouldn't affect performance much. A stripesize can only really be too small; not too large. Random I/O (read+write) works best on larger stripesizes, to make sure one I/O will be handled by only one disk and not multiple because the data overlaps multiple disks.

I often hear a large stripesize is bad for small files; where in fact its the exact opposite.
July 15, 2009 6:51:54 PM

Stripe size can have a huge affect on performance especially smaller files, and larger files usually have little impact from stripe size because typically you will be reaching a hardware limitation.
July 17, 2009 2:26:03 AM

http://www.vmware.com/pdf/vi_performance_tuning.pdf

i would suggest you ask your VMware presales engineer out to lunch and pick his brains clean. stripe size is only 1 of serveral MAJOR considerations when planning and implementing your VMware environment. esp when using iSCSI.

one thing to note, ESX doesn't do MPIO, it only does it in failover. ESX 4 supports 3rd party MPIO, but there is usually licensing costs to this. we were supprised when the evil mahcine company doubled the price of their MPIO software just for ESX.

i would really suggest getting on the VMware forums. best to ask the target audience.
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