Windows 2008 Hyper-V R2 Background Merge

When you remove a snapshot or snapshot subtree from a Hyper-V VM, there is a merge process that combines the data in the .avhd snapshot file back into the VM's VHD.

In Windows 2008 RTM, the merge process only happened once the virtual machine was shut down. The VM was unavailable for the duration of this process. There was, however, a progress bar displayed in either SCVMM or Hyper-V Manager that would indicate the completion percentage.

In Windows 2008 R2, however, the merge process happens in the background. Any indication of it happening is no longer easily visible in the console.

To view the progress of a merge, run the following PowerShell command:

Get-WmiObject -Namespace "root\virtualization" -Query "select * from Msvm_ConcreteJob" | Where {$_.ElementName -eq 'Merge in Progress'}

This will give you output about all merges happening, the elasped time (in seconds, so be prepared to do some math), as well as the job completion percentage.