I have a client with a Windows 2008R2 Hyper-V parent, and guest VMs. I was preparing to upgrade their Altaro Hyper-V software from version 4 to version 5, when I discovered that there was a single, stray snapshot file (.avhd) for one of the guest VMs. The strange thing is that the Hyper-V console was not showing that any snapshots exist or had been created for this VM.

I did some poking around, and buried in this Microsoft forum post was a response from Pablo which worked perfectly for me. His response is dated January 28, 2014.

Here are the steps he recommended and that I performed (again this was on a 2008 R2 Hyper-V server):

• Shutdown the VM in question
• On the right frame of the Hyper-V click on Snapshot and create a new snapshot. You can confirm this by going to the folder where the .avhd file exists, and you should now see a second .avhd file.
• Return to the Hyper-V console, and from the middle frame, right click on the snapshot and select to delete the snapshot.
• Over on the right frame you will see a message that a merge is in process.
• Once the merge is completed, both .avhd files had been automatically removed from the folder location.