Hyper-V Host is 2012 R2 with several guests.
My primary guest is a TFS server using a 100G VHD. I wasn't really keeping track of it that close and at some point the VHD hit 100% space used. I expanded the size by 20G, but the space used remained at 100%.
So I begin trying to understand how to fix the issue by asking why did the 20G I added not leave me with open space on the VHD?