Read Response time vs Read Miss response time.
I am looking into possible performance issues on a meta lun that is on EFD disk on my VMAX. The LUN has a SQL2008 DB on it. I am getting complaints from the SQL team that the disk is "slow". I find it hard to belive being on flash but ok. I have been looking at SPA and ECC Performance manager. During the "slowness" the I/O profile is have random reads. I have been looking at the read response time and read miss response time. I know a read miss goes to disk and not cache. The read miss response time is under 2ms consistently. Great! However the read response time goes anywhere from 2ms to 50ms! Unfortunatly SPA and Performance manager shows in 5min increments so I can get much more granular for how long it spikes.
My main question is... Is read miss response time just how long it takes the VMAX to go to disk for the I/O, or is it calculating the time that the I/O comes in, cant find in cache, goes to disk, then back to the FA? Why would the read response time be so much higher then the read miss? Is 20-50ms something to even be concerned about?
The I/O profile of the LUN is consistent. It has been doing these spikes from the begnning it seems but now that they are looking at it closely i just want to make sure the 20-50ms spike isn't causing issues.
Thanks for your help!