Hyper-V introduced a new feature called “snapshot” that allow you to capture and save the point in time state of a running or saved virtual machine and then go back to that state at a latter point in time. When a snapshot is taken we create a new differencing disk to point the virtual machine to and we call it an AVHD or automatic VHD since it was created automatically by requesting the snapshot. When you delete a snapshot the next time the virtual machine is off or saved we will merge the AVHD created by the snapshot back into it’s respective parent…  We do this automatically and in the background – so lets say you wanted to know when it’s was done programmatically…  It’s not too hard just run the following query to see if any merges are going on presently - PS C:> Get-WmiObject -Namespace "rootvirtualization" -Query "select * from Msvm_ConcreteJob" | Where {$_.ElementName - eq 'Merge in Progress'}. 

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