Hyper-V VM stuck in endless loop trying to merge deleted snapshot with insufficient disk space

Solution 1:

Turning RAID off seems like a Bad Idea™, but you're pretty well suck unless you can plug a USB drive into the server or something like that. You can shutdown the machine, cancel the merge, the grab the vhd and avhd files. Once you move them Hyper-V will no longer merge them automatically, you'll have to do it manually. Once it's merged move the vhd back to the original location and Hyper-V will automatically pickup that the avhd file is gone.

Solution 2:

Rename all the AVHD associated with the virtual server to VHD

It comes from a method of manually merging snapshots which might work.

I haven't tried this method so I take no responsibility if it messes up. If you have an external backup, I suggest you take one :)

Reference to manually merging disks

http://www.virtualizationadmin.com/kbase/VirtualizationTips/ServerVirtualization/MicrosoftHyper-VR2Tips/General/ManuallyMergingHyper-VSnapshots.html