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Assigning Virtual CPU settings VMware 5.1

Posted on 2014-12-26
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I am trying to assign virtual cpu settings in VMWare 5.1 I don't know why but can't get my head around the settings.

I have a 2 X quad core HP DL380 G5 server and I have a SBS2003 virtual machine

How should I configure the cpu settings

Number of virtual sockets and
Number of cores per socket.

I just am not sure what setting relates to the physical sockets

I assume 2 physical CPUs and 8 cores (being quad core each) is this correct


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Question by:cdsaus
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Andrew Hancock (VMware vExpert / EE MVE^2) earned 1600 total points
ID: 40518390
Always ASSIGN virtual sockets! for you SBS server I would assign at least 2 vCPU or 4 vCPU.

1 vCPU = approx 1 physical core on the host!

(only assign Cores in the VM, if you have a license restriction on cores!)

vSMP (virtual SMP) can affect virtual machine performance, when adding too many vCPUs to virtual machines that cannot use the vCPUs effectly, 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
http://www.vmware.com/resources/techresources/10131

see here
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/

also there is a document here about the CPU scheduler

www.vmware.com/files/pdf/perf-vsphere-cpu_scheduler.pdf

https://blogs.vmware.com/vsphere/2013/10/does-corespersocket-affect-performance.html
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by:gheist
gheist earned 400 total points
ID: 40519081
Virtual cores are to get around licencings in some software (e.g you might want to buy 2-core licence of CAD software, so you must make sure it gets you right.

Flying to land of 5.5 -> virtual core setting also causes problems with vNUMA unless it is 1:1 match to hardware.
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Author Closing Comment

by:cdsaus
ID: 40531187
Thanks for information, it has solved my problem and given me a greater insight. Great links to information
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