Number of Processors Question

[MikeGIllinois]

As always, thanks for the help I get out here.

I have a simple question. If I have a Quad Core machine then I have four processors available to assign to VM's I create.

Can I assign 2 processors to VM A and 2 to VM B and 4 to VM C? 2 + 2 + 4 = 8. Is this ok to do?

I've been thinking that if I have 4 processors available I can only assign, for instance, 1 processor to each of four VM's. Is this incorrect?

Thank you.

Mike Gallery

[weinstein5]

Yes you can overcommit the CPUs in your ESX/ESXi host with vSphere 4 you can average 4-8 vCPUs per core- Its impact on performance is going to depend on the CPU load required by the VM - also to point out best practice is always to start with a single vCPU and add additional if needed -

[MikeGIllinois]

Thank you for that answer.

I notice that if I attempt to edit the settings of a VM and change the processor count from 1 to 2 or more I get a warning about risking the stability of the VM. I once added another processor to an XP VM and had no problems. When I rebooted XP just found "additional hardware" and worked fine. Can I up the processors on Windows Server 2008 or other higher ended Windows Server products?

Also, I note you mention 4 to 8 processors per core. Are you saying that if I have a Quad Core CPU I could, conceivably, have 4 VM's each with 8 processors?

Thank you.

Mike Gallery

[weinstein5]

That is more of a generic warning in that older version of WIndows and other operating systems ustilized HALs that specific to uni or multi processor machines and if ythey were not changed to match uni or smp would cause stability or performance issues - 

[danpalacios]

2008 is very stable when it comes to changing the physical properties.  In fact, you can hot add cpu and memory if you set the VM properties ahead of time (Options > Advanced > Memory/CPU Hotplug).  I have played with this and had no problems with the VM at all.