I would like to understand better the possibilities of VmWare ESXi memory overcommitment. I've read this paper from VmWare, so I am familiar with general concepts, such as hypervisor swapping, memory balooning and page sharing. It seems that a combination of these techniques allows for quite a large degree of overcommitment. However, I am not sure.

I am deploying a virtual test lab comprising of 4 identical sets of virtual servers and workstations and a couple of virtual router instances. Overall, I expect to be running around 20 virtual machines with Windows XP, Windows 7 and Ubuntu for workstation hosts as well as CentOS and Windows 2008 Server instances for servers.

The problem is, however, that the host machine only has 12GB of RAM and I don't have an option to stuff in some more. I would like to know what is the best option to configure hosts in order to achieve reasonable performance within the constrains.

I have these two options:

• Allocate as little as possible of RAM to each virtual machine.
• Allocate an extraordinary amount (such as 4 GB per instance) and let the baloon driver do the rest.
• Something else?

Which would work better? Machines will mostly be idle, so I don't have any major performance expectations, but they should run reasonably smoothly nevertheless.