number.read is unset

Hi all,

trying to monitor IOPS with number.read & write; how ever it doesn't return anything...

Statistics level is set to 3 and when i browse the mob and run the following QueryPerf :

<querySpec xsi:type="PerfQuerySpec">

  <entity type="ManagedObject">vm-XXX</entity>

  <!--optional-->

  <startTime>2013-07-24T00:00:00Z</startTime>

  <!--optional-->

  <endTime>2013-07-25T00:00:00Z</endTime>

  <!--optional-->

  <!--array start-->

  <metricId xsi:type="PerfMetricId">

    <counterId>128</counterId>

    <instance></instance>

  </metricId>

  <!--array end-->

</querySpec>

I get the following:

Method Invocation Result: PerfEntityMetricBase[]

Name Type Value

name string "Return value"

val PerfEntityMetricBase[]

Name Type Value

dynamicProperty DynamicProperty[] Unset

dynamicType string Unset

entity ManagedObjectReference:VirtualMachine vm-XXX (Node3)

sampleInfo PerfSampleInfo[] Unset

value PerfMetricSeries[] Unset

Any idea why the numberread is Unset and how can i enable it ?