Storage Latency on ESX host

[diddler99]

Hi, I notice that latency on an ESXi 5.1 host shows latency of 30ms. This is showing for the DAVG. The KAVG does not show anything. However when I check the response time on the Unisphere for VMAX the response time does not go over 5ms.

Does anyone know what might be causing this discrepancy between both values?

How does the ESX host get this value?

[Alistar]

Hi there,

although I have no insight into the VMAX solution, I can only tell you that the values you are seeing are:

• DAVG - this stands for Device Average and is a value that is gathered directly from the disk array
• KAVG - is the Kernel Average and dictates how much time the hypervisor took to process your I/Os

Hope it helps you at least a little bit

[diddler99]

Thanks for reply Allstar. Yea it's just that on the vmax the response time is described as been the exact same as DAVG. However when I check the latency on the host it would be 30ms whereas on the vmax the 'response time ' is 3ms. So not sure where the difference is.

[mikejroberts]

I see similar differences in our environment and have found it to be more accurate if I display the "Maximum" values in Unisphere - by default it shows averages.  Also, the way I understand it, DAVG is from the HBA to the storage and back.  So it is possible that some of that latency is not just the VMAX.  I am not sure the counters between Unisphere and esxtop or vCenter are going to align 100% since they collect at different intervals.