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Difference between 2 vCPU sockets and 1 vCPU sockets w/ 2 cores

Posted on 2011-09-19
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Last Modified: 2012-05-12
In vsphere 5, does a windows guest think there is any difference if you assign 2 vCPU sockets with 1 core, than if you assigned 1 vCPU socket with 2 cores? With vsphere 5 you can now separate out the cores. Thanks
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Question by:fina27
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LVL 119
ID: 36560617
1 vCPU = 1 Core on the physical processor (but it could be a different core due to the scheduler)
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by:fina27
ID: 36560646
But the guest still thinks its 2 cores regardless of either config right? So does it technically not matter?
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Andrew Hancock (VMware vExpert / EE MVE^2) earned 500 total points
ID: 36560749
The guest has no knowledge of what a core is. To the guest it's a vCPU. The guest thinks it's 2 vCPU, which may be the same physical Cores, unless you physically allocate them.

Personally I would leave the settings alone, unless you have a real reason to allocate specific cores to a VM, and let the Hypervisor complete the scheduling for the VM.

With vsphere 5 you can now separate out the cores

You've always been able to do it, but now there is a new GUI, that may make it easier, rather than selecting Advanced CPU Affinity Options in vSphere 4.0.
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Netscaler Common Configuration How To guides

If you use NetScaler you will want to see these guides. The NetScaler How To Guides show administrators how to get NetScaler up and configured by providing instructions for common scenarios and some not so common ones.

 
LVL 119
ID: 36560776
I've not seen the ESX 5.0 whitepaper yet, but this is for 4.1.

check it out

VMware vSphere 4: The CPU Scheduler in VMware ESX 4.1
http://www.vmware.com/files/pdf/techpaper/VMW_vSphere41_cpu_schedule_ESX.pdf
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by:fina27
ID: 36560812
What do you mean by leave the settings alone? So if i was building a new windows server and wanted to give it 3 vCPU's, would I select 3 virtual sockets and 1 core each or 1 virtual socket and 3 cores?

If your answer is it depends, then what is it depending on? Thanks
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LVL 119
ID: 36560897
Just allocate 3 vCPUs, and let the hypervisor schedule the vCPU across the total cores in the phsyical host.

Also remember that adding additional vCPU can also slow a virtual machine down to due the vSMP scheduling.
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LVL 119
ID: 36561014
Using multicore virtual CPUs can be useful when you run operating systems or applications that can take advantage of only a limited number of CPU sockets.

Chapter 4 of the Resource Management Guide explains in more details

http://pubs.vmware.com/vsphere-50/topic/com.vmware.ICbase/PDF/vsphere-esxi-vcenter-server-50-resource-management-guide.pdf
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