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mouyaq
Contributor
Contributor

high kernel latency in SQL MSCS

Hello,

I have a problem with a MSCS, i have a physical - virtual cluster running SQL instances and have very high kernel latencies, between 400 - 1200 ms. There is no much IOPs but anyway the are very high kernel latencies and also QUED and LOAD are higher than 1.

The luns presented to ESXi have Round Robin as PSP and have this version "VMware ESXi 5.1.0 build-799733"

The hba parameters are:

     Emulex LightPulse FC SCSI 10.0.727.24

     Emulex LPe12000-M8 8Gb PCIe Fibre Channel Adapter

     Firmware Version: 2.01A12 (US2.01A12)

     Current speed 8G

Do you anything to improve this performance??

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DavoudTeimouri
Virtuoso
Virtuoso

Hi,

Emulex driver can issue 30 IOPs by default and ESXi issue 32 IOPs when a LUN is shared by VMs.

So if your Storage array support huge IOPs, you can increase your HBA queue depth and also your "Disk.SchedNumReqOutstanding".

BR

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Davoud Teimouri - https://www.teimouri.net - Twitter: @davoud_teimouri Facebook: https://www.facebook.com/teimouri.net/
lvaibhavt
Hot Shot
Hot Shot

Hi,

VMware does not support RR PSP for any LUN which is a part of MSCS in ESXi 5.1.

This issue has been sorted out in ESXi 5.5. Please refer to below article

VMware KB: Changing a LUN to use a different Path Selection Policy (PSP)

""""However, in some configurations, such as MSCS using shared storage RDMs (Raw Device Mappings), you need to change the Path Selection Policy (PSP) because Round Robin PSP is not supported for MSCS Clustering prior to vSphere 5.5""""""""""""""""""


Change it to MRU and check if this helps.




Thanks

mouyaq
Contributor
Contributor

I will try to change it. Can i change queue length without restart the host?

I tought that vsphere5 had adaptative queue length so i wouldn't have to change that because it increase automatically....

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mouyaq
Contributor
Contributor

Thanks lvaibhavt, just before write this comment, i'd changed from RR to MRU, also i'd marked RDM luns as perennally  too.

This change from RR to MRU appears to improve the performance, but we haven't do a serious test yet. I think it will on next Monday so i'll tell you if works, if not i'll try to change what says


Thanks

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