LucD notes

Since ESX 4u1 you have a new SCSI controller type available for your guests, the VMware Paravirtual SCSI Controller.
From several sources we learn that the performance of this controller is better.

See for example the New !! Open unofficial storage performance thread where Lars gave some interesting performance figures.

And in the PowerCLI Community there is a recent thread, called Change SCSI adapter to paravirtual with PowerCLI, where the user asks how he can change his disk adapters.

Reason enough to look how I could use PowerCLI to migrate guests to the VMware Paravirtual SCSI Controller.

The script uses the well-known ReconfigVM_Task method to make the change. It will change any existing SCSI controller, whose name is specified in the $ctrlName variable, to a VMware Paravirtualization SCSI controller.

Make sure the correct driver is installed in the Windows guest OS before you run the script to change the controller that hosts your boot device, otherwise the OS will BSOD !

Update August 20th 2010: A thread in the PowerCLI Community from Benj informed me that the script didn’t work any more in  vSphere 4.1. It seems that API 4.1 requires the ControllerKey and UnitNumber of the new Paravirtual SCSI Controller to be specified. The script has been updated.

The script

$vmName = "MyVM"
$ctrlName = "SCSI controller 0"

$vm = Get-VM $vmName | Get-View

# Get the controller and the devices connected to it
$vm.Config.Hardware.Device | where {$_.DeviceInfo.Label -eq $ctrlName} | % {
	$oldCtrl = $_
	$ctrlKey = $_.Key
	$devs = @()
	$_.Device | % {
		$devKey = $_
		$vm.Config.Hardware.Device | where {$_.Key -eq $devKey} | % {
			$devs += $_
		}
	}
}

# Create the specification for the device changes
$spec = New-Object VMware.Vim.VirtualMachineConfigSpec

# Remove old controller
$old = New-Object VMware.Vim.VirtualDeviceConfigSpec
$old.device = $oldCtrl
$old.operation = "remove"
$spec.DeviceChange += $old

# Update the devices connected to the controller
$devs | % {
	$dev = New-Object VMware.Vim.VirtualDeviceConfigSpec
	$dev.device = $_
	$dev.device.ControllerKey = -100
	$dev.operation = "edit"
	$spec.DeviceChange += $dev
}

# Add new controller
$new = New-Object VMware.Vim.VirtualDeviceConfigSpec
$new.Device = New-Object VMware.Vim.ParaVirtualSCSIController
$new.Device.Key = -100
if($defaultVIServer.Build -ge '258902'){
	$new.Device.ControllerKey = $oldCtrl.ControllerKey
	$new.Device.UnitNumber = $oldCtrl.UnitNumber
}
$new.operation = "add"
$spec.DeviceChange += $new

$vm.ReconfigVM($spec)

Line 8: remember the ‘old’ controller

Line 10-16: collect all devices that are connected to the controller

Line 19-42: populate the VirtualMachineConfigSpec object with all the changes

Line 22-26: remove the ‘old’ controller

Line 28-35: change the ControllerKey for all the devices that were connected to the ‘old’ controller. As stated in the SDK documentation, you may not reassign keys in your script. To avoid this problem, use a temporary key which the system will replace by the new key. Use a negative integer for the temporary key.

Line 37-48: create the new controller. Note that the vSphere system will pick up the devices that were connected to the old controller and will updated their ControllerKey property to point to the new controller.

Line 41-44: test if the script is running in a vSphere 4.1 environment (build 258902 or higher). If it is, fill in the ControllerKey and UnitNumber properties.

The VMware Paravirtual SCSI Controller is currently only supported on a limited set of guest operating systems. See KB Article: 1010398 for the list and also for some other limitations.

Note that you can not use a VMware Paravirtual SCSI Controller on a guest that you have configured for Fault Tolerance.

Although there are some limitations, I still hope the script is useful to some of you.