When you create a snapshot, the current state of the vm is preserved by leaving the disk files alone. All changes since the moment of creating the snapshot are written to delta files. The delta files are stored in the vm’s working directory. The working directory is – by default – the location where the vmx and other config files reside. If that datastore runs out of free space – especially if it also contains disk files – you’re in a bit of a kerfuffle. Vms not booting or being frozen as if they stared into Medusa’s reptoid eyes.

So you can do two things: reserve overhead in your datastores and stay afraid some overactive snapshot might destroy your environment, or set the working directory of your vms to some big-ass datastore you don’t use for anything else and let the snapshots enjoy themselves. If they fill up the datastore, they only kill all vms with snapshots, not the rest.

But how, you ask? You can edit the vmx files of you vms manually - which requires your vms to be powered down – and add the line: workingDir = “/vmfs/volumes/<insanely long guid you need to somehow find>/”

Or, you run my script and change the working location on the fly:

# Description:
# Set's the Working Location for a VM. This location will hold the vswap and snapshot delta files.
 
# Usage:
# First, connect to a virtual server server (Connect-VIServer)
#
# Set snapshot location for one vm (folder must already exist on datastore):
# Set-VMSnapshotLocation -vm VM001 -Location "[BigAssDatastore] Snapshots"
#
# For all vms at once (no folder specified will put all in the root of the datastore):
# Get-VM | ForEach-Object {Set-VMSnapshotLocation -vm $_ -Location "[BigAssDatastore]"}
#
# Reset the location to the original location (with the vmx file):
# Set-VMSnapshotLocation -vm VM001 -Reset
 
Function Set-VMSnapshotLocation
	{
	param($vm, [string]$Location, [switch]$Reset=$False)
 
	#Region Input Validation
	# Check vm parameter
	If (!$vm)
		{
		Throw "No VM specified."
		}
	# Check Location parameter.
	# Can be empty when using Reset, can be "[datastore]" or can be "[datastore] folder" (folder must exist).
	If (!$Reset -and $Location -notmatch "\[\S+\](\s\w+)?")
		{
		Throw "Invalid location specified. Syntax: [Datastore] Folder"
		}
	# Specifying Reset will set Location to empty, which causes the original location to be used (same location as vmx file).
	If ($Reset)
		{
		$Location = ""
		}
	# Make sure to get a vm object to work with.
	# This allows both using a vm name when targeting one vm (Set-VMSnapshotLocation -vm VM001 -Reset);
	# AND piping a collection of vm's (Get-VM | ForEach (Set-VMSnapshotLocation -vm $_ -Location "[BigAssDatastore] Snapshots" ).
	If ($vm.GetType().Name -eq "String")
		{
		$oVM = Get-VM $vm
		}
	ElseIf ($vm.GetType().Name -eq "VirtualMachineImpl")
		{
		$oVM = $vm
		}
	Else
		{
		Throw "Parameter vm is of an invalid type."
		}
	#EndRegion InputValidation
 
	#Region Main
	# Get advanced properties of vm
	$vmView = $oVM | Get-View
	# Create object containing new properties
	$vmConfigSpec = New-Object VMware.Vim.VirtualMachineConfigSpec
	$vmConfigSpec.Files = New-Object VMware.Vim.VirtualMachineFileInfo
	$vmConfigSpec.Files.SnapshotDirectory = $Location
	# Reconfigure VM using new properties
	$vmView.ReconfigVM($vmConfigSpec)
	#EndRegion Main
	}

You can download it here: Set-VMSnapshotLocation (rename to .ps1)

I tried hard as I could, but I could not get my vm to die. Even running the script, creating a snapshot, running the script to move the working location again and deleting the snapshot did not prove a problem. However, I urge you to be careful with it. I’m not responsable for anything you do with it.

Tiny glitch: the VI Client shows the wrong datastore location when a vm has a snapshot in a modified workingdir.

Enjoy.

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$VCServerName = “MYVCSERVER”
$VC = Connect-VIServer $VCServerName
$SI = Get-View ServiceInstance
$CFM = Get-View $SI.Content.CustomFieldsManager

Take a look at the $CFM.Field property. It contains an array of available fields. Next step: add our own custom field.

# Variables
$CustomFieldName = “Snapshots”
$ManagedObjectType = “VirtualMachine”
# Check if the custom field already exists
$myCustomField = $CFM.Field | Where {$_.Name -eq $CustomFieldName}
If (!$myCustomField)
{
# Create Custom Field
$FieldCopy = $CFM.Field[0]
$CFM.AddCustomFieldDef($CustomFieldName, $ManagedObjectType, $FieldCopy.FieldDefPrivileges, $FieldCopy.FieldInstancePrivileges)
}

Final step: Fill the custom field with some relevant information:

# Fill Custom Fields
$VMs = Get-VM
$VMViews = $VMs | Get-View
ForEach ($VMView in $VMViews)
{
$SnapshotCount = ($VMView.Snapshot.RootSnapshotList | Measure-Object).Count
If ($SnapShotCount)
{
$VMView.setCustomValue($CustomFieldName,$SnapShotCount)
}
}

Now take a look at the VI Client:

More examples coming soon!
Hugo

PS: Don’t forget to schedule the script to run at an interval, so the values are kept up-to-date!

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Is there a way (preferably a one-liner) to get a list of vm’s and the number of snapshots per vm?

Here’s a script that will get that info:

$VC = Connect-VIServer $VCServerName
$vms = Get-VM
$myCol = @()
ForEach ($vm in $vms)
{
  $snapshots = Get-Snapshot -VM $vm
  $myObj = "" | Select-Object VM, NumSnapshots
  $myObj.VM = $vm.name
  $myObj.NumSnapshots = ($snapshots | measure-object).count
  $myCol += $myObj
}
$myCol | Where-Object{$_.NumSnapshots -gt 0} | Sort-Object VM | Format-Table -AutoSize

And here’s a one-liner that does the same thing: 

Get-VM |
  Where{(Get-SnapShot -VM $_ | Measure-Object).Count -gt 0} |
  Format-Table Name, `
  @{Label="NumSnapshots";Expression={(Get-Snapshot -VM $_ | Measure-Object).Count}}

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