What is the maximum CPU can be assigned to per VM

[jwpang]

Hi,

Can anyone please advice me what is the maximum CPU can be assigned to per VM. My ESX host specification as follow:

Processor Socket: 4

Core Per Socket: 4

Logical Processor: 16

Thanks.

Regards,

Nicholas

[schepp]

Hi and welcome to the communities.

It depends on your ESXi version.

Prior to 5.5 the maximum vCPU was dependant on the vSphere license you used.

In 5.5, this limit is gone and you can assign vCPUs up to the physical limit of the host or the limit mentioned in the vSphere Maximum configuration doc.

If you have 5.5, you can assign 16 vCPU per VM with that host.

[JPM300]

ESXi 5.5 has the abillity to go up to 64 vCPU per VM assuming your host has the CPU to can handle it:

http://www.vmware.com/pdf/vsphere5/r55/vsphere-55-configuration-maximums.pdf

Since you have 16 logical CPU in your host before hyper-thredding I would say 16vCPU should be the highest you should go.  Anything past 16vCPU will give the CPU scheduler a harder time.  As nice as hyperthreded cores are I never count on them when designing or assign vCPU to a VM. 

[williambishop]

Be aware though, there are other realities at play here, you should be aware of numa boundaries and how they affect performance.

[JPM300]

Very true, however anything past 8 vCPU will automatically turn on NUMA so it sorts it out.   Anything <= 8vCPU you have to do some fine tweaking to get best results.