I’ve been trying to figure out how to allocate RAM for our guest-servers, and how much is needed for the host. I thought this was a static number, and have been pretty much running it on instinct, usually leaving 2-3GB for my hosts.
As it turns out, it’s a bit more complicated. Memory should be spread out as such:
300 MB for the Hypervisor plus 32 MB for the first GB of RAM allocated to each virtual machine plus another 8 MB for every additional GB of RAM allocated to each virtual machine plus 512 MB for the host operating system running on the root partition
Digital Library World has a nice calculator for us here: http://digitallibraryworld.com/?p=55