What happens if I start a virtual machine that is merging snapshot files? [Hyper-V]

If you have a virtual machine with snapshots that have been deleted, it might decide to start merging in the snapshot AVHD files the next time the virtual machine turns off.  But what if you were only planning to turn off the virtual machine for 5 minutes while you made some configuration changes?

Well, the good news is that you can still start up the virtual machine.  Starting the virtual machine will cancel the merge operation and the virtual machine will start and function correctly.  The bad news, however, is that when you start the virtual machine all progress made on the merge operation will be thrown away.  The next time the virtual machine shuts down the merge will start over again – from the beginning.  This means that in order for the snapshot files to merge in successfully you need to ensure that the virtual machine is offline for the entire amount of time for the merge operation to complete.