The XenServer VSS Provider is useful for taking quiesced snapshots and facilitating backups of running VMs.

The XenServer VSS Provider is included in the XenServer Tools, but it is not installed by default.

Perform a 'repair install' of Citrix XenServer VSS Provider if the script is missing.

Browse to and execute as an administrator:

C:\Program Files (x86)\Citrix\XenTools\install-XenProvider.cmd

Reboot for the changes to take effect.

We have seen where the (unsupported) Citrix XenVSS service frequently stops running, but will restart on demand.

Here is an importable scheduled task for Windows Server 2012 R2 to restart the XenVSS service on a schedule. Modify as necessary.

Extract Then Import the XML File

<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.4" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
  <RegistrationInfo>
    <Date>2015-12-29T10:50:50.8563628</Date>
    <Author>YOURDOMAIN\administrator</Author>
  </RegistrationInfo>
  <Triggers>
    <CalendarTrigger>
      <StartBoundary>2015-12-29T21:55:00</StartBoundary>
      <Enabled>true</Enabled>
      <ScheduleByDay>
        <DaysInterval>1</DaysInterval>
      </ScheduleByDay>
    </CalendarTrigger>
  </Triggers>
  <Principals>
    <Principal id="Author">
      <UserId>S-1-5-18</UserId>
      <RunLevel>HighestAvailable</RunLevel>
    </Principal>
  </Principals>
  <Settings>
    <MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
    <DisallowStartIfOnBatteries>true</DisallowStartIfOnBatteries>
    <StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
    <AllowHardTerminate>true</AllowHardTerminate>
    <StartWhenAvailable>false</StartWhenAvailable>
    <RunOnlyIfNetworkAvailable>false</RunOnlyIfNetworkAvailable>
    <IdleSettings>
      <StopOnIdleEnd>true</StopOnIdleEnd>
      <RestartOnIdle>false</RestartOnIdle>
    </IdleSettings>
    <AllowStartOnDemand>true</AllowStartOnDemand>
    <Enabled>true</Enabled>
    <Hidden>false</Hidden>
    <RunOnlyIfIdle>false</RunOnlyIfIdle>
    <DisallowStartOnRemoteAppSession>false</DisallowStartOnRemoteAppSession>
    <UseUnifiedSchedulingEngine>false</UseUnifiedSchedulingEngine>
    <WakeToRun>false</WakeToRun>
    <ExecutionTimeLimit>P3D</ExecutionTimeLimit>
    <Priority>7</Priority>
  </Settings>
  <Actions Context="Author">
    <Exec>
      <Command>C:\Windows\System32\net.exe</Command>
      <Arguments>start "XenVss"</Arguments>
    </Exec>
  </Actions>
</Task>