##############################
# Script created by Hugo Peeters #
# http://www.peetersonline.nl   #
##############################

# Variables
$VCServerName = "MYVCSERVER"
$CustomFieldName = "Snapshot Size (MB)"
$ManagedObjectType = "VirtualMachine"

# Script
$VC = Connect-VIServer $VCServerName
$SI = Get-View ServiceInstance
$CFM = Get-View $SI.Content.CustomFieldsManager

$myCustomField = $CFM.Field | Where {$_.Name -eq $CustomFieldName}
If (!$myCustomField)
	{
	# Create Custom Field
	$FieldCopy = $CFM.Field[0]
	$CFM.AddCustomFieldDef($CustomFieldName,$ManagedObjectType,$FieldCopy.FieldDefPrivileges,$FieldCopy.FieldInstancePrivileges)
	}
	
# Fill Custom Fields
$VMs = Get-VM
$VMViews = $VMs | Get-View
ForEach ($VMView in $VMViews)
	{
	$SnapshotCount = ($VMView.Snapshot.RootSnapshotList | Measure-Object).Count
	# Measure Disk Usage of Snapshot
	$SnapshotDirectory = $VMView.Config.Files.SnapshotDirectory
	$DatastoreName = $SnapshotDirectory.Split("[] ")[1]
	$ds = Get-Datastore -Name $DatastoreName | Get-View
	$fileQueryFlags = New-Object VMware.Vim.FileQueryFlags
	$fileQueryFlags.FileSize = $true
	$searchSpec = New-Object VMware.Vim.HostDatastoreBrowserSearchSpec
	$searchSpec.details = $fileQueryFlags
	$dsBrowser = Get-View $ds.browser
	$searchResult = $dsBrowser.SearchDatastoreSubFolders($SnapshotDirectory, $searchSpec)
	$totalSize = [Math]::Round(($searchResult[0].File | Where {$_.Path -match "delta" -or $_.Path -match "snapshot"} | Measure-Object FileSize -Sum).Sum/1MB,0)
	# Compare value to current value
	If ($totalSize -ne ($VMView.CustomValue | ?{$_.Key -eq $myCustomField.Key}).Value)
		{
		# Set Custom Value
		$VMView.setCustomValue($CustomFieldName,$totalSize)
		}
	}
Disconnect-VIServer -Confirm:$False