Modifying Hyper-V Server settings with WMI

Here is a little thing that I recently put together to modify Server level settings of my Hyper-V Server.  Most of my focus so far has been on the VMs themselves, why not tweak the server?

Why might you need to change settings of the Hyper-V server itself?  Um, because you can, and therefore you should.  You might need to change the MAC address range, or the default path, or some other crazy thing.

What can you change?

Well, first, you have to get the Msvm_VirtualSystemManagementServiceSettingData WMI object.  This class is the settings of the hypervisor and things that the management OS must keep in check.

If you get the WMI object and then type it out in the PowerShell windows you will see something like this:

__GENUS                    : 2
__CLASS                    : Msvm_VirtualSystemManagementServiceSettingData
__SUPERCLASS               : CIM_SettingData
__DYNASTY                  : CIM_ManagedElement
__RELPATH                  : Msvm_VirtualSystemManagementServiceSettingData.InstanceID="Microsoft:BJEDAR2"
__PROPERTY_COUNT           : 13
__DERIVATION               : {CIM_SettingData, CIM_ManagedElement}
__SERVER                   : BJEDAR2
__NAMESPACE                : root\virtualization
__PATH                     : \\BJEDAR2\root\virtualization:Msvm_VirtualSystemManagementServiceSettingData.InstanceID="Microsoft:BJEDAR2"
BiosLockString             :
Caption                    : Hyper-V Virtual System Management Service
DefaultExternalDataRoot    : C:\Users\Public\VMs\
DefaultVirtualHardDiskPath : C:\Users\Public\VMs\
Description                : Settings for the Virtual System Management Service
ElementName                : Hyper-V Virtual System Management Service
InstanceID                 : Microsoft:BJEDAR2
MaximumMacAddress          : 00155D748DFF
MinimumMacAddress          : 00155D680A00
NumaSpanningEnabled        : True
PrimaryOwnerContact        :
PrimaryOwnerName           : Administrators
ScopeOfResidence           :

Now, how can I do something useful with this?  Read on.  I am going to modify the MAC address range of the host.

First, you have to get an instance of the Virtual Machine Management Service as this will give you the method you need to actually modify the WMI objects.  If you don’t do this, you only have a bunch of read only properties through CIM.

$VMManagementService = Get-WmiObject -Namespace root\virtualization -Class Msvm_VirtualSystemManagementService -ComputerName $hypervHost

Now, I want to get the object I typed out above:

$vsmssd = Get-WmiObject Msvm_VirtualSystemManagementServiceSettingData -Namespace "root\virtualization" -ComputerName $hypervHost

And see the MAC address range:

$vsmssd.MinimumMacAddress
$vsmssd.MaximumMacAddress

Then change the value:

$vsmssd.MaximumMacAddress = “00155D74FFFF”

Then put the change:

$VMManagementService.ModifyServiceSettings($vsmssd.psbase.gettext(1))

A return value of “0” is success, a return of “4096” is generally a long running job or something went bad.