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LUN with high response times ? How to fix?

Hi All

Im having a performance issue with one of my applications and traced down the cause I think - I just dont know how to fix it so if any one has any ideas I would really appreciate it.

Scenario:  Large SQL server, virtualised on ESX 5.0, running a VNX 5500 unified, large 3 tier storage pool, with FASTVP & FASTcache (1000GB) Flare 32 patch 015

One of the LUNs attached to the server shows high response times at times >40ms, we also get high device and kernel latency at the ESX level, during those periods the write size of the IO is high 128KB+.  Read size is variable, but large read sizes with tiny writes doesnt have the same impact on latency.

From what Ive read writes that size are going to be bypassing FASTCache ?  Is this correct?

What can I do to improve performance with the large write size coming through ?

Oh yes.. critical high profile project being affected - as always!


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