Details about "disk read queue length" and "disk write queue length" RRS feed

  • Question

  • Hi, 

    I need to understand whether the values reported by Perfmon (Windows Server 2003) include the active I/Os (i.e. the ones which are in progress) plus the ones waiting to start, or just the ones waiting to start.

    Is there any way to determine how many I/Os Windows will start to a device at once?

    Wednesday, November 19, 2008 8:45 PM


  • Hi Ted,

    Disk I/O performance counters will show you the active+queued I/O - whatever is in flight - but only as long as I/O request made it to the volume manager. Any I/O that is in flight to the volume manager wouldn’t be exposed until the next perf counter sample.

    If you are using Windows Vista (and later), to take a closer look at the I/O activity on the system capture a trace using xperf that is part of the Windows Performanc Toolkit (available for download at using:
        xperf -on DiagEasy
        ... run scenario ...
        xperf -d trace.etl

    Then open the trace with

        xperf trace.etl

    and examine the disk activity using the Disk utilization/activity graphs and corresponding summary tables.
    Saturday, November 22, 2008 5:31 AM