Counting CPUs

[shane_presley]

We have a Dell 1950 with 2 quad core CPUs. I know as far as VMware's license, I only need to buy a 2CPU license.

But when it comes to the guest VMs, how do they see the CPUs? Will I be able to present up to 8 CPUs to any VM? Or can I only present 2 CPUs (and those will be multicore CPUs)?

Thanks, Shane

[brekus · Accepted solution]

Correct, you will only need to buy a 2CPU license. In ESX 3.5 you can only have 4 virtual CPU's assigned to a VM. Check out page 2 of the maximums config guide http://www.vmware.com/pdf/vi3_35/esx_3/r35/vi3_35_25_config_max.pdf . When you present virtual CPU's to a VM, you are in a sense presenting "cores" if you assign 1vCPU the VM will only use 1 core when it needs it. If you assign it 2vCPU's, it will use 2 cores at the same time when it is running any processes.

[mcowger]

You need a 2 socket license.

You will be able to present 1, 2 or 4 cores to any given VM.

--Matt

[shane_presley]

Excellent explanation, thanks guys

So given that, I could oversubscribe the CPUs right? In an 8 core box, I could have 10VMs, each with 1 core assigned. That would be 10 cores assigned even though I only have 8, but ESX will manage the resources to share the CPUs?

[mcowger]

Yes, you can (and probably SHOULD) over subscribe. One of our current clusters has 128 cores and 260 virtual CPUs allocated in it.

--Matt