Suspicious value from WMI Win32_PerfRawData_PerfOS_PagingFile PercentUsage figure.

Question

I've written a little VBScript program to query the page file usage under Windows XP (eventually 2003/2008 Server as well) but the figures I seem to be getting are bizarre.

This is the program:

Set wmi = GetObject("winmgmts:{impersonationLevel=impersonate}!\\.\root\cimv2")
for i = 1 to 10
    Set qry1 = wmi.ExecQuery ("Select * from Win32_PageFileSetting")
    Set qry2 = wmi.ExecQuery ("Select * from Win32_PerfRawData_PerfOS_PagingFile")
    initial = 0
    maximum = 0
    For Each obj in qry1
        initial = initial + obj.InitialSize
        maximum = maximum + obj.MaximumSize
    Next
    For Each obj in qry2
        if obj.Name = "_Total" then
            Wscript.Echo _
                " Initial size: " & initial & _
                " Maximum size: " & maximum & _
                " Percent used: " & obj.PercentUsage & _
                ""
        end if
    Next
    qry1 = none
    qry2 = none
    WScript.sleep (1000)
Next

which outputs:

Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354
Initial size: 1512 Maximum size: 3024 Percent used: 21354

The doco on MSDN states:

PercentUsage
    Data type: uint32
    Access type: Read-only
    Qualifiers:
        DisplayName ("% Usage")
        CounterType (537003008)
        DefaultScale (0)
        PerfDetail (200)
    Percentage of the page file instance in use. For more information,
    see the PageFileBytes property in Win32_PerfRawData_PerfProc_Process.

Now that seems pretty straight-forward. Why is my 3G page file using 21000% of it's allocated space? That would be about 630G but pagefile.sys is only about 1.5G (and my entire hard disk is only 186G).

---

Update:

When I get the same field from Win32_PerfFormattedData_PerfOS_PagingFile, I get a more reasonable value of 5 but that still doesn't seem to coincide with Task Manager, which shows 1.06G usage out of the 3G maximum.

Answer 1

You can't operate with the value directly like that.

The CounterType of the ProcessUsage property is 537003008, which according to this table corresponds to the PERF_RAW_FRACTION counter. Given the formula from the second link, we end up with something like this:

" Percent used: " & ((obj.PercentUsage * 100) / obj.PercentUsage_Base) & _