Q. I'm deleting a Hyper-V virtual machine (VM) that had snapshots. Why is the VM delete taking so long?

A. This problem ties into how snapshots work with Hyper-V. Remember that when you create a snapshot, the configuration, memory, and supporting process information is saved and a differencing disk is created to store future disk changes. When you delete a VM, all the snapshots are deleted. However, the virtual hard disk (VHD) is not deleted, which means all content stored in the differencing disks associated with the snapshots must be merged with the original VHD, as the following diagram shows.

What takes most of the time when you delete a VM with snapshots, then, isn’t the deletion itself but the merging all the differencing disks associated with the snapshots. This merging process ensures that the VHD that remains after the deletion contains all the disk-based content at the point the VM was deleted.