By default, Windows is set to wait 20 seconds for a service to gracefully shut down before it is terminated during a host system shutdown. While in most cases this isn't a big deal, it is a bit of an issue when you are running Virtual Server or Hyper-V and need to wait for all the VMs to enter a saved state before the host shuts down.

Typically, when a Virtual Server or Hyper-V host OS enters shutdown mode and it sends the Stop command to the Virtual Server or Hyper-V services, it will attempt to place all guest VMs into a saved state, essentially freezing whatever they are doing at that moment, and saves the memory to disk so it can be rapidly resumed when the host comes back up (Think Hibernation). Until this is completed, the Virtual Server or Hyper-V services will not enter the stopped state. However, depending on how much memory is allocated to a guest VM that needs to be written to disk or how many guest VMs are entering a saved state and competing for disk I/O, this process may (and probably will) take more than 20 seconds. What happens if the guest VMs can't be saved in time? Think of the effect as "pulling the plug" on the guest VM. It is shut off ungracefully and the contents of memory are lost much like what happens if you pull the plug out of the back of a running server.

Thankfully, there is a way to lengthen the amount of time Windows will wait for services to enter the stopped state before ending them ungracefully. This is done by opening up trusty RegEdit and navigating to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control where you will find WaitToKillServiceTimeout set to a default of 20000 milliseconds. Double click on WaitToKillServiceTimeout and change the value to a larger number, such as 180000 (3 minutes) and then click OK and close RegEdit. This will tell Windows to wait for 3 minutes for the service to enter the Stopped state before ending it ungracefully. This should give your guest VMs plenty of time to enter the Saved state before a host system shutdown.

NOTE: This setting affects ALL services. So, if the Virtual Server or Hyper-V services have finished stopping but another services is hanging, Windows will wait for the time you specified before killing the service. Keep this in mind if you wonder why Windows isn’t shutting down even though Virtual Server or Hyper-V are all stopped.