You have a task to extend virtual hard disk of Hyper-V VM, but the type of disk is “Differencing”. That means you have checkpoint (snapshot) attached to this VM. If it’s manually created checkpoint, you can delete it from Hyper-V manager. But sometimes delete option is not available, because the checkpoint was created by backup system (DPM) and usually it called “VM Name – Backup – Date”
It’s quite easy to merge checkpoint with virtual disk using Powershell commands. You have to run it directly on Hyper-V host where VM is running.
The following command will help you determine that a checkpoint is currently available on the VM:
Get-VMSnapshot -VMName vmname.net -ComputerName hyper-vhost.net| fl
This command will get and delete checkpoint from specified VM:
Get-VMSnapshot -VMName vmname.net -ComputerName hyper-vhost.net| Remove-VMSnapshot