Tag Archives: WMI

Which Disk is that volume on?

I administer a server VM with a lot of disks, and many of them are the same size. When I need to make changes to the system’s storage, I’m always nervous that I’m going to poke the wrong disk. I could trust that the order of the disks listed in the vSphere client is the same as the order that the guest OS lists (starting at 1 and 0 respectively). But I want a little more assurance.

Using diskpart, you can list the details for individual disks, partitions and volumes, but I wanted a report showing all the disks, the partitions on those disks, and the volumes residing on those partitions. I have reported some of this info previously, using PowerShell’s Get-WMIObject cmdlet to query the Win32_DiskDrive, Win32_Partition, and Win32_Volume classes. I figured there must me a way to correlate instances of these classes.

I found these two blog posts:

They did most of the heavy lifting in building the WQL ASSOCIATOR OF queries. I put together a short script to give me a little more detail. Here’s some sample output:

PS C:localscripts> .Get-DiskInfo.ps1
Disk 0 - SCSI 0:0:2:0 - 45.00 GB
    Partition 0  100.00 MB  Installable File System
    Partition 1  44.90 GB  Installable File System
        C: [NTFS] 44.90 GB ( 3.46 GB free )
[...]
Disk 5 - SCSI 0:0:2:5 - 39.99 GB
    Partition 0  40.00 GB  Installable File System
        B: [NTFS] 40.00 GB ( 34.54 GB free )

This will make it easier to be sure about the vSphere storage element that corresponds to a particular volume (or, more accurately, the Physical Disk on which the volume resides).

Here’s the actual script:

 .Get-DiskInfo.ps1

.NOTES
    Author: Geoff Duke 
    Based on http://bit.ly/XowLns and http://bit.ly/XeIqFh
#>

Set-PSDebug -Strict

Function Main {

    $diskdrives = get-wmiobject Win32_DiskDrive | sort Index

    $colSize = @{Name='Size';Expression={Get-HRSize $_.Size}}

    foreach ( $disk in $diskdrives ) {

        $scsi_details = 'SCSI ' + $disk.SCSIBus         + ':' +
                                  $disk.SCSILogicalUnit + ':' +
                                  $disk.SCSIPort        + ':' +
                                  $disk.SCSITargetID
        write $( 'Disk ' + $disk.Index + ' - ' + $scsi_details +
                 ' - ' + ( Get-HRSize $disk.size) )

        $part_query = 'ASSOCIATORS OF {Win32_DiskDrive.DeviceID="' +
                      $disk.DeviceID.replace('','\') +
                      '"} WHERE AssocClass=Win32_DiskDriveToDiskPartition'

        $partitions = @( get-wmiobject -query $part_query | 
                         sort StartingOffset )
        foreach ($partition in $partitions) {

            $vol_query = 'ASSOCIATORS OF {Win32_DiskPartition.DeviceID="' +
                         $partition.DeviceID +
                         '"} WHERE AssocClass=Win32_LogicalDiskToPartition'
            $volumes   = @(get-wmiobject -query $vol_query)

            write $( '    Partition ' + $partition.Index + '  ' +
                     ( Get-HRSize $partition.Size) + '  ' +
                     $partition.Type
                   )

            foreach ( $volume in $volumes) {
                write $( '        ' + $volume.name + 
                         ' [' + $volume.FileSystem + '] ' + 
                         ( Get-HRSize $volume.Size ) + ' ( ' +
                         ( Get-HRSize $volume.FreeSpace ) + ' free )'
                       )

            } # end foreach vol

        } # end foreach part

        write ''

    } # end foreach disk

}

#--------------------------------------------------------------------
function Get-HRSize {
    [CmdletBinding()]
    param(
        [Parameter(Mandatory=$True, ValueFromPipeline=$True)]
        [INT64] $bytes
    )
    process {
        if     ( $bytes -gt 1pb ) { "{0:N2} PB" -f ($bytes / 1pb) }
        elseif ( $bytes -gt 1tb ) { "{0:N2} TB" -f ($bytes / 1tb) }
        elseif ( $bytes -gt 1gb ) { "{0:N2} GB" -f ($bytes / 1gb) }
        elseif ( $bytes -gt 1mb ) { "{0:N2} MB" -f ($bytes / 1mb) }
        elseif ( $bytes -gt 1kb ) { "{0:N2} KB" -f ($bytes / 1kb) }
        else   { "{0:N} Bytes" -f $bytes }
    }
} # End Function:Get-HRSize

Main

Please let me know if you find this helpful.

Semisynchronous WMI

Experimenting with querying WMI from Perl with Win32::OLE, I ran across the following WMI query options in an Perl example from Microsoft’s Script Center:

$colItems = $objWMIService->ExecQuery ("SELECT * FROM Win32_Share","WQL",wbemFlagReturnImmediately | wbemFlagForwardOnly); 

After some digging, I found the following explanation of those options wbemFlagReturnImmediately, and wbemFlagForwardOnly:

Because WMI manages the object, semisynchronous mode is more secure than asynchronous mode. However, if you use semisynchronous mode with more than 1,000 instances, instance retrieval can monopolize the available resources, which can degrade the performance of the program or script and the computer using the program or script. Each object takes up the necessary resources until the memory is released.

To work around this condition, you can call the method with the iFlags parameter set with the wbemFlagForwardOnly and wbemFlagReturnImmediately flags to instruct WMI to return a forward-only SWbemObjectSet. A forward-only SWbemObjectSet eliminates the performance problem caused by a large data set by releasing the memory after the object is enumerated.

[from: http://msdn.microsoft.com/en-us/library/aa384832(v=vs.85).aspx ]

I wanted to put this somewhere, because I’m sure I’ll forget.