Hyper-V: Scripting Dynamic VHD Creation

Today I would like to show you some basic scripts for creating a new dynamically expanding virtual hard disk.  The tricky thing about doing this is that the WMI interfaces for creating virtual hard disks expect the size of the new virtual hard disk to be specified as a UINT64.  This requires some special handling - but can be done in both VBScript and PowerShell.

VBScript:

 Option Explicit

 'Setup constant to use for getting the right value for the new VHD size

 const Size1G = &H40000000

 Dim HyperVServer

 Dim VHDName

 Dim VHDSize

 Dim WMIService

 Dim Msvm_ImageManagementService

 Dim Result

 Dim Job

 Dim InParam

 Dim OutParam

 'Prompt for the Hyper-V Server to use

 HyperVServer = InputBox("Specify the Hyper-V Server to create the dynamic virtual hard disk on:")

 'Get name for VHD

 VHDName = InputBox("Specify the name of the new dynamic virtual hard disk:")

 'Get size for VHD

 VHDSize = InputBox("Specify the size of the new dynamic virtual hard disk (in GB):") * Size1G

 'Get an instance of the WMI Service in the virtualization namespace.

 Set WMIService = GetObject("winmgmts:\\" & HyperVServer & "\root\virtualization")

 'Get the Msvm_ImageManagementService object

 Set Msvm_ImageManagementService = WMIService.ExecQuery("SELECT * FROM Msvm_ImageManagementService").ItemIndex(0)

 'Setup the input parameter list

 Set InParam = Msvm_ImageManagementService.Methods_("CreateDynamicVirtualHardDisk").InParameters.SpawnInstance_()

 InParam.Path = VHDName 

 InParam.MaxInternalSize = VHDSize

 'Execute the method and store the results in OutParam

 Set OutParam = Msvm_ImageManagementService.ExecMethod_("CreateDynamicVirtualHardDisk", InParam) 

 'Check to see if the job completed synchronously

 if (OutParam.ReturnValue = 0) then

    Wscript.Echo "The virtual hard disk has been created."

 elseif (OutParam.ReturnValue <> 4096) then

    Wscript.Echo "The virtual hard disk has not been created."

 else   

    'Get the job object

    set Job = WMIService.Get(OutParam.Job)

     'Wait for the job to complete (3 == starting, 4 == running)

    while (Job.JobState = 3) or (Job.JobState = 4)

       Wscript.Echo "Creating VHD. " & Job.PercentComplete & "% complete"

       WScript.Sleep(1000)

       'Refresh the job object

       set Job = WMIService.Get(OutParam.Job)

    Wend

    'Provide details if the job fails (7 == complete)

    if (Job.JobState <> 7) then

       Wscript.Echo "The virtual hard disk has not been created."

       Wscript.Echo "ErrorCode:" & Job.ErrorCode

       Wscript.Echo "ErrorDescription:" & Job.ErrorDescription

    else

       Wscript.Echo "The virtual hard disk has been created."

    end If

 end if

PowerShell:

 # Setup constant to use for getting the right value for the new VHD size

 [UInt64]$Size1G = 0x40000000

 # Prompt for the Hyper-V Server to use

 $HyperVServer = Read-Host "Specify the Hyper-V Server to use (enter '.' for the local computer)"

 # Get name for VHD

 $VHDName = Read-Host "Specify the name of the new dynamic virtual hard disk"

 # Get size for VHD

 [UInt64]$VHDSize = Read-Host "Specify the size of the new dynamic virtual hard disk (in GB)" 

 # Get the Msvm_ImageManagementService object

 $ImageManagementService = gwmi Msvm_ImageManagementService -namespace "root\virtualization" -computername $HyperVServer

 # Compact the VHD

 $result = $ImageManagementService.CreateDynamicVirtualHardDisk($VHDName, $VHDSize * $Size1G)

 #Return success if the return value is "0"

 if ($Result.ReturnValue -eq 0)

    {write-host "The virtual hard disk has been created."} 

 #If the return value is not "0" or "4096" then the operation failed

 ElseIf ($Result.ReturnValue -ne 4096)

    {write-host "The virtual hard disk has not been created.  Error value:" $Result.ReturnValue}

   Else

    {#Get the job object

     $job=[WMI]$Result.job

     #Provide updates if the jobstate is "3" (starting) or "4" (running)

     while ($job.JobState -eq 3 -or $job.JobState -eq 4)

       {write-host "Creating. "$job.PercentComplete "% complete"

        start-sleep 1

        #Refresh the job object

        $job=[WMI]$Result.job}

      #A jobstate of "7" means success

     if ($job.JobState -eq 7)

        {write-host "The virtual hard disk has been created."}

       Else

        {write-host "The virtual hard disk has not been created."

         write-host "ErrorCode:" $job.ErrorCode

         write-host "ErrorDescription" $job.ErrorDescription}

    }

Cheers,

Ben