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VMware ESXi - Physical Processor Support

Posted on 2010-03-24
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We are in the process of setting up a new ESXi server on our single CPU system.  We are concerned, however, about the processor requirements and limitations in ESXi.  Unfortunately, VMware's website and documentation do not seem to give a clear-cut answer about how many physical processors are allowed to be used in ESXi.  They do indicate that it supports up to 64 logical cores, but that does not answer the question of the processor itself.

How many physical processors can be used in ESXi?  Can we install ESXi in a 2 CPU system?

Thanks in advance.
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Question by:geteke
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by:coolsport00
ID: 28463402
Yes you can. Here is VMware's Config Max Guide that can confirm what you can have:
http://www.vmware.com/pdf/vsphere4/r40/vsp_40_config_max.pdf

~coolsport00
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by:geteke
ID: 28465661
Thank you for the response.

It indicates how many "VIRTUAL" CPUs you can have and how many "LOGICAL" processors you can have.  That still does not answer how many physical processors you can have, as in a processor that I can physically pull off the motherboard if I wanted.

Does "LOGICAL" mean "PHYSICAL"?
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by:coolsport00
ID: 28467212
I believe that's just 'wording', which I agree...it's poor. I want to confirm that though first, so I reply in a few to let you know. But, to answer your question, yes, you can have 2 CPUs...that is fine (this, I know). My question is the max, which is pretty high (the '64' number is close to accurate).

~coolsport00
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by:jakethecatuk
ID: 28467344
The physical processor is the piece of silicon that sits inside the server.

The logical processor count would be the number of cores and hyper threading.  For example, if a server is sold as being QUAD CORE, then means that ESXi would see four logical processors.  If the server had hyper threading, then ESXi would see another four logical processors giving eight processors.  Add another CPU, and it would see sixteen logical processors.  As you can see, eight physical processors using the above would give you the maximum of sixty four logical processors.

Most low/medium end servers have the capacity for either two or four processors.
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by:coolsport00
ID: 28469101
He's referring to the documentation "jake...". Logical is ok...it's explained in the Guide. VMware just doesn't use "physical" in it (why, I don't know).

~coolsport00
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coolsport00 earned 1000 total points
ID: 28483633
OK "geteke", this is what I found out from VMware:
"There is no exact number of the maximum physical CPUs a host can have. It all depends on the number of cores within the processor that is being installed in the host. Unfortunately our Configuration Maximums Guide specifies the number cores, because our products utilize the cores rather than the physical CPU. It all comes down to what you are putting into the host, whether it be single, dual, or quad core processors."

So, for example, the last column of the Computer Max. section under ESX in the Guide says "Virtual CPUs per physical core". What this means is:
Basically,
        -Single Core = 1 physical CPU
        -Dual Core = 2 cores (1 Physcial CPU)
        -Quad Core = 4 cores (1 physical CPU)

Depending on the number of cores your ESX host has will help determine the amount of Virtual CPUs you have, and if that will remain under the Maximum Virtual CPUs per host. ESX does not read how many physical CPU's the host carries, but rather how many Cores it can utilize. So, going back to the "Virtual CPUs per Physical Core" item, this means that for a single core, you can have 20 Virtual CPUs. If you have a single, dual-core CPU, you can have 40 Virtual CPUs; a single, quad-core = 80 vCPUs; 2 single-core = 40 vCPUs, etc.

Hope that helps. I'm getting explicit clarification on what exactly is meant by Virtual CPU in the Guide though.

~coolsport00
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by:Paul Solovyovsky
ID: 28484975
the difference between virtual CPUs and Logical CPUs is as such

1 Quad core = 4 virtual CPUs.  If the quad core supports hyperthreading than you'll see 8 logical CPUs as each virtual cpu will have 2 threads.

Hope this helps.
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by:coolsport00
ID: 28567886
Hi "geteke"...thanks for the points! :) I wanted to provide the final 'answer' from VMware engineers as I mentioned I was going to do. To further expound, this is what their answer is on Virtual CPUs (for the most part, what "paul..." said) :)

"A Virtual CPU is a segment of the 'core' created by the VMkernel in ESX to help prevent one small virtual machine from using up an entire core to itself.

You'll notice that the Configuration Maximums displays that you can have up to 20 vCPUs per core. Basically if you have 2 Virtual Machines using only 500Mhz of CPU each, the VMKernel will read this and create two vCPUs under one core (for example: 2.4Ghz) and use 1000Mhz of that 2.4Ghz."

A Virtual CPU is what I thought it was (vCPU = a VMs allocated CPU designated by ESX; more specifically speaking, by the VMkernel). My confusion was why they took out max. PHYSICAL CPUs in their Guide. The answer to that is because VMware technology now (actually...since ESX3.x) looks at Cores instead of sole physical sockets.

Hope that further helps.

~coolsport00
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