I’m using a lab box with 9GB RAM in it for testing to see what sort of load I can get out of a Hyper-V host. Remember that Hyper-V does not do memory over-committing like you get on ESX – who really wants paging both in the virtual machine’s virtual disk and on the physical host? That sounds like server admin hell to me!
Anyway, I managed to get a series of virtual machines up and running, each with varying RAM assignment to reflect a production environment. The result was that I got 7GB of VM’s up and running on the 9GB host. It appears that a full installation of Windows Server 2008 with RC1 of Hyper-V consumes 2GB RAM. That probably comes down if you use a core installation instead, which I’d recommend in a Hyper-V farm.
Cool thing here is that I noticed no drop in performance. The VM’s all run quite smoothly – we’re doing all sorts of things with the VM’s so they are actually doing real (albeit just lab) work.
EDIT:
I followed this post up with some research on the memory overhead requirements and how Hyper-V uses RAM.