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disk perfmon counter "avg sec/write" values not looking consistent with graph

  • February 24, 2016 at 11:34 pm

    #311719

    Hi All,

    I had a support call to troubleshoot slow performance on the SQL server and I did see a lot of PAGEIOLATCH waits and suspected disk issues.

    I've setup perfmon counters avg sec per write, per read and collected the dataset for one hour during business hours.

    I have a graph which suggests that each write took around 40 milliseconds to complete. But the min, avg and max suggest very low values on the bottom right hand corner in the uploaded picture. Is this a bug in windows server 2008 R2 OS, which one is correct, is it the graph or the values at the bottom right side?

    Thanks in advance

  • February 24, 2016 at 11:42 pm

    #1860965

    Just to add I've also noticed quite a few logwrite waits, hence added the avg sec/write counter as well. The graph in question is for this counter.

  • February 25, 2016 at 12:06 am

    #1860966

    you should better read this[/url] before going forward.

  • February 25, 2016 at 12:39 am

    #1860968

    The counter shown in the graph isn't the one you have selected at the bottom. The avg disk sec/read firstly is in red, the counter on the graph is blue, second the avg disk sec/read has it's 'show' checkbox unchecked, it's not shown on the graph.

    Basically you're looking at two different things and wondering why they're not the same.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

  • February 25, 2016 at 1:36 am

    #1860974

    Hi Gail,

    Thank you for the response,

    Actually, that was an RDP session and I unfortunately could not get all of that pane into the snip capture.

    I have deliberately unchecked the sec/read counter as I just wanted to see the avg sec/write (in blue) only. Trust me, I have only that counter checked. We cannot see that here because its below that avg sec/read counter and as I said, I was not able to capture that in the screenshot.

    The graph is only for avg secs/write/

  • February 25, 2016 at 2:06 am

    #1860982

    Can you reduce perfmon to a window size you can capture the entire of and repost the screenshot?

    Don't uncheck counters, use the highlight option in the toolbar to emphasise the one that you're looking at. It's often useful to compare the counter value you're looking at with the other ones shown.

    Gail Shaw
    Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
    SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

    We walk in the dark places no others will enter
    We stand on the bridge and no one may pass

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