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Datastore Contention

Posted on 2014-10-15
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Hi Experts,

Hoping you can clear something up for me. What is the easiest way to distinguish between poor disk performance of a disk array, and data contention produced by too many VM's per host per datastore

Would i be right in saying a comparision between datastore latency and the latency of the vms on that datastore would shed such light? Ie if the datastore latency is low by the vm latency is high it would indicate a point of contention?

Kind Regards
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Question by:FSIFM
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Andrew Hancock (VMware vExpert / EE MVE^2) earned 2000 total points
ID: 40381756
Yes, that's the correct approach, check the latency of the VM on the datastore, using esxtop and if greater than 10ms, that VM is having issues with the datastore.

Then change RAID type, (RAID 6 to RAID10) disk type (SATA to SAS, or SAS to SSD)

let me know if you need help with esxtop.
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by:FSIFM
ID: 40381766
Fantastic :)

We have tools to monitor vm latency and the datastore latency already, but my main problem was isolating what was contention and what was the disk array not providing enough performance for the requirement.

If i can just look at the datastore, see it is sitting below 10ms but the vm is 20+ then that points me in the right direction of too many vms on that datastore creating a choke point as aposed to fearing the arrays don't have enough iops to keep up with demand
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Yes, 20ms is higher than the recommended 10ms for a VM.

Baseline the VMs, if it is always this high, if so, you have options above, and moving VM to faster datastore, or change datastore.
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