Best Practice Server CPU, 2vCPU or 1vCPU?

[VCPGuru]

We configure every Microsoft W2k3 and W2k8 server with 2vCPU, because we heard that this is a "Best Practice" value. Whats your opionion? Any docs from VMware to this topic?

Any help would be appreciated!

[ChrisDearden · Accepted solution]

Where did you hear this ?

The reverse is more often the case - only give 2 VCPU's to workloads that need it ( Exchange / SQL / Terminal Servers are the only ones I've seen any benefits from it ) having multiple vCPU's reduces our consolidation ratio on a farm considerably.

[vmroyale]

Use as few vCPUs as possible.

Supporting documentation: http://www.vmware.com/pdf/vi_performance_tuning.pdf - page 3

[RParker]

Agree with other 2 posters, as a practical matter virtualizing more CPU is a bad idea unless you absolutely can prove you need it. Virtual CPU's cause more overhead on the server, and they don't give more CPU cycle/power as a result, most often. So unless your performance of VM's is suffering NEVER give more CPU than you NEED.

[weinstein5]

I am throwing my voice in with the chorus - always start with a single vCPU - add extra only if absolutely necessary - the reason for this is how the vmkernel schedules the vCPU's - they are scheduled simultaneously so if the vmkernel can not schedule all vCPU in a virtual smp vm none will get scheduled - think of it this way it is easier to schedule 1 vCPU vs 2 CPUs vs 4 -

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[miveli]

I have another question for this thread. What is the stance of everyone on the number of vCPU's to CPU's? I have a 12 host ESX 3.5 U3 cluster with 96 pCPU's and we just finished a analysis of the environment's capacity. We have 90 vCPU's in play at the moment. I am of the opinion that you should have 1 vCPU per pCPU core for the production environment and feel that we can only get 6 more servers into the environment before we run into bottlenecks/problems. My managers disagree (they went to a HP expo recently). We have already exceeded the physical memory capacity as well so 6 more machines i feel will leave us exposed on host performance and HA/DRS if we loose a host.

I would really appreciate some opinions