Running VMware in VMware?
We have a physical machine that runs VMware and hosts a VM we use for SharePoint deployment testing. That machine is old and dying, and my employer's network czars are heavily pushing hosted VMs as a replacement for outdated physical servers. I was curious about whether it's possible to run VMware inside VMware, and if so, whether there are severe performance implications. We don't require extreme performance from this setup, since it's just used for SharePoint testing and the associated SQL Server is on a different box. My guess is that we can't just use the primary hosted VM for our testing because we'll want to roll back occasionally and otherwise have more control over it, and getting buy-in for that from the network folks is unlikely. Does anyone have any experience with this?
edit: I know this nesting certainly isn't the preferred option, but (1) we want the flexibility of being able to use VMware snapshots at will and (2) the network folks will not allow us to arbitrarily roll back to a previous point in time because of the potential for removing mandated security updates. My guess is that a local desktop machine running VMware Workstation might just be the way to go. The hosted option seems attractive if it will work though since it's less machine maintenance for me to deal with.
Answer
The technical limitation with running VMware inside VMware is that VMware, Virtual PC, etc takes advantage of the Virtualization features present in modern CPUs.
If you have two or more hypervisors are both trying to control Ring 0 then there will be problems, this is something that I've encountered while trying to run both VMware and Virtual PC simultaneously on my desktop - one will error out/crash.
If your hypervisor can interact with the 'parent' hypervisor, then you'll be OK. Alternatively if the child hypervisor doesn't try to use the CPU virtualization features, or entirely emulates the CPU (such as QEMU) then you should also be OK.
Basically old-style hypervisors on old CPUs use Full virtualization (slow) which would be capable of nesting with a heavy, heavy performance hit. modern Hypervisors/CPUs use hardware assisted virtualization (near native performance) and you'd be hard pressed to find a hypervisor that is designed or capable of nested virtual machines.
Finally, I'd really advise against running dev/test VMs on the same physical server that is running production VMs. There's just too much to go wrong and security implications - you need to manage the dev/test environment and it sounds like you shouldn't have access to production environment. Likewise you probably don't want the operations team messing about with your test environment.
UPDATE: ESXi 4 now supports virtualizing itself. See this article for more information