Guest Quiescing explained

When doing image based backups with vRanger you have the option to enable Guest Quiescing under backup options.

This means that vRanger request VMware tools to initiate a Windows Volume Shadow Copy Service (VSS) snapshot in the Guest OS.

All registered VSS writers (run vssadmin list writers command to list all writers) in the Guest OS get the request and they prepare its application to be backed up (committing all transactions to disk).

Once all VSS writers are finished they communicate back to vRanger which then initiate a VMware snapshot. This will make the backup application consistent.


In order for this to work the VMware Tools VSS component must be enabled and Legato Sync Driver must be disabled (if present).

If your VM was created prior ESX 3.5 U2 you might have issues with incorrect drivers!

You can verify by initiating a VMware Tools Upgrade in interactive mode - Modify - Verify Volume Shadow Copy Service is enabled and if Sync Driver is present to disable it.

If you are familiar with Microsoft PowerShell and VMware PowerCLI you can run the following script to query all your Windows VMs (this will be done over WMI and requires you to have administrative rights to remote systems) for both Legato Sync Driver and VSS.


Get-VM | Where {($_.PowerState -eq "PoweredOn") -and ($_.Guest.OSFullName -like "Microsoft Windows*")} | Sort Name | Select Name, @{N="LGTO Installed";E={((Get-WmiObject Win32_PnpEntity -ComputerName $_.Guest.HostName -Filter "Service='LGTO_Sync'" | Measure-Object).Count -gt 0)}}, @{N="VSS Installed";E={((Get-WmiObject Win32_Service -ComputerName $_.Guest.HostName -Filter "Name='vmvss'" | Measure-Object).Count -gt 0)}}


Thanks to:

Sample output from script:


What level of consistency do I get?

That depends on what version of vSphere you are running and what Guest OS you have.

* Special requirements for application consistency on Windows 2008/R2, see below.

  • Dynamic Disks are not supported
  • SCSI disks only
  • UUID attribute must be enabled.
    • Enabled default on VMs created on vSphere 4.1
    • VMs created on prior vSphere 4.1, following procedure must be followed:
      • Power off your Windows 2008 VM
      • Edit Settings - Options - General - Configurations Parameters - Add Row - Name=disk.EnableUUID Value=true


To make sure all your VMs have Legato Sync Driver Disabled, VSS Enabled and disk.EnableUUID configured correctly will take a serious amount of time if you have to connect to each VM manually and verify everything.


Introducing Quest PowerGUI

There is a much better and easier option available for you (free of charge). Quest PowerGUI is an application that is easy to use combined with the power of PowerShell scripting without the need to be a scripting wizard. Scripts are provided in different preloaded PowerPacks and you can easily extend the functionality by adding more PowerPacks from PowerGUI Library or write your own custom scripts as well.

You must have Microsoft PowerShell and VMware PowerCLI installed before you install PowerGUI, make sure you use PowerCLI 4.0 U1 as later versions has backward compatibility issues with many scripts.

You can use PowerGUI to manage your VMware environment more efficient such as finding snapshots, memory limits, connected CD-roms etc. It´s easy to find and reconfigure settings in bulk mode.

With help from Kirk Munro aka Poshoholic and Scott Herold aka VMguru I made a PowerPack that you can import (File - PowerPack Management - Import - Browse to VSS Status.powerpack) to PowerGUI and it will list status of Legato Sync Driver, VSS and disk.EnableUUID for selected VMs.

Select any VMs and Click VSS Status.

Results can be exported to XML, CSV and HTML. You can click on any of the columns to sort it.

Supported Applications:

Most Microsoft applications (AD, Exchange, SQL Server, Share Point), Oracle and others has a VSS writer and can be backed up in an application consistent state when using vRanger.