This article describes the steps needed to manually take a Volume Shadow Copy on your Hyper-V Host using the Microsoft Diskshadow command from Windows command prompt.


Firstly, launch Command Prompt as Administrator (with elevated privileges), then run the following commands:

diskshadow
set verbose on
set context volatile (Deletes the shadow copy on exit or reset)
add volume c: (always include this)
add volume XXXX (replace with the volume containing your VM's VHDXs)

Note: Repeat to add each volume that contains files associated with your VMs


begin backup
create 


After entering the “create” command the shadow will be created. If it fails it will provide information regarding why it failed.

If it succeeds you can then end the test with the command:

end backup
exit


References: 

Diskshadow command information on Technet: https://technet.microsoft.com/en-us/library/cc772172.aspx


You may log the output of this command by using /l

For example: diskshadow /l C:\diskshadow.log