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VM configuration formula related to Socket and Cores

Posted on 2016-09-02
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I need to have a better understanding as to how best to configure VMs.

Need to specifically understand  how Number of VIrtual Sockets and Number of Cores per Socket needs to be configured? - What are the things I need to consider. (e.g. ESXi configuration)

Is there some sort of formula or specific guideline, I can follow.
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Question by:cgeorgeisaac
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Andrew Hancock (VMware vExpert / EE MVE^2) earned 500 total points
ID: 41781612
Summary from the document below...

#1 When creating a virtual machine, by default, vSphere will create as many virtual sockets as you’ve requested vCPUs and the cores per socket is equal to one. I think of this configuration as “wide” and “flat.” This will enable vNUMA to select and present the best virtual NUMA topology to the guest operating system, which will be optimal on the underlying physical topology.

Source

Important Reading here

Does corespersocket Affect Performance?

Allocate as many vCPUs that you require, and if you need to use Cores based on licensing conditions use cores. But the VMware vSphere Default of using vCPU (sockets) is best.

You should have a rough idea, of the server/application requirements.

vSMP (virtual SMP) can affect virtual machine performance, when adding too many vCPUs to virtual machines that cannot use the vCPUs effectively, e.g. Servers than can use vSMP correctly :- SQL Server, Exchange Server.

This is true, many VMware Administrators, think adding lots of processors, will increase performance - wrong! (and because they can, they just go silly!). Sometimes there is confusion between cores and processors. But what we are adding is additional processors in the virtual machine.

So 4 vCPU, to the VM is a 4 Way SMP (Quad Processor Server), if you have Enterprise Plus license you can add 8, (and only if you have the correct OS License will the OS recognise them all).

If applications, can take advantage e.g. Exchange, SQL, adding additional processors, can/may increase performance.

So usual rule of thumb is try 1 vCPU, then try 2 vCPU, knock back to 1 vCPU if performance is affected. and only use vSMP if the VM can take advantage.

Example, VM with 4 vCPUs allocated!

My simple laymans explaination of the "scheduler!"

As you have assigned 4 vCPUs, to this VM, the VMware scheulder, has to wait until 4 cores are free and available, to do this, it has to pause the first cores, until the 4th is available, during this timeframe, the paused cores are not available for processes, this is my simplistic view, but bottom line is adding more vCPUs to a VM, may not give you the performance benefits you think, unless the VM, it's applications are optimised for additional vCPUs.

See here

VMware vSphere: The CPU Scheduler in VMware ESX 4.1

also there is a document here about the CPU schedule

Does corespersocket Affect Performance?

see here also

http://www.gabesvirtualworld.com/how-too-many-vcpus-can-negatively-affect-your-performance/

http://www.zdnet.com/virtual-cpus-the-overprovisioning-penalty-of-vcpu-to-pcpu-ratios-4010025185/
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Author Comment

by:cgeorgeisaac
ID: 41781678
Great Links. Thanks.
I am not too sure if you want me to open another question, but this is the issue:

We have a machine which has  Win Server 2012 64  which is very slow.

VM Ver 8
CPU: Number of Virtual Socket=4 and Number of Cores per socket = 1. Therefore, Total Number of Cores is 4

Memory 8192 MB
Running  VMTools Out of date (unable to install latest since we have vCenter 6.x)
How could this be fixed.
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LVL 120
ID: 41781725
Best to post a new question, on the issue of a slow VM.
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