CPU Allocation Hyper V

Posted on 2013-11-03
Last Modified: 2016-11-23
Dear Experts,

I have Dell Server with 4 Physical Processor,12 Logical Processor each and 6 cores.

I have dedicated this server for Hyper-V

I need to understand how many maximum processor I can assign to a virtual machine.

I would highly appreciate any help.

Question by:cciedreamer
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LVL 37

Expert Comment

ID: 39619617
for Windows 2012, it is 64.

FYI - Hyper-V Scalability in Windows Server 2012
LVL 25

Assisted Solution

by:Mohammed Khawaja
Mohammed Khawaja earned 100 total points
ID: 39619635
4 for Win2K and 64 for Win2K12.
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Author Comment

ID: 39619620
BTW, I am using Windows 2008.

Author Comment

ID: 39619640
What is the concept of processor allocation to guest operating system ?

What are these virtual processor and are they allocated from the physical one ?

Since I have 4 Physical Processor,12 Logical Processor each and 6 cores, why I can't assign more ?

Please help me to understand the cpu allocation.
LVL 121

Accepted Solution

Andrew Hancock (VMware vExpert / EE MVE^2) earned 400 total points
ID: 39619787
the relationship, is kind of

1 virtual CPU = 1 Core on the physical processor.

but it may not be the same core on the physical processor.

Author Comment

ID: 39619903
Thanks for the reply.

I didn't get by this

"but it may not be the same core on the physical processor."

Please can you give me some explanation.
LVL 121

Assisted Solution

by:Andrew Hancock (VMware vExpert / EE MVE^2)
Andrew Hancock (VMware vExpert / EE MVE^2) earned 400 total points
ID: 39619992
no problems, in sumple terms, my simplified understanding is the hypervisor algorythym shifts the process from core to another core on the physical processor, depending upon load on the physical CPU.

so you power on the VM, and the VM's 1 vCPU could be using core#0, but five minutes later it could be shifted to core#5.

the above is simplified, this is really happening in mirco seconds. Hence you workload is scheduled using the cpu scheculer across multipe cores on the host cpu. It's also scheduled to take advantage of under-used cores on the physical processor.

Author Comment

ID: 39620379
I have found this great article. The author has given excellent explanation..
What I have understood 1 core = 1 Virtual Processor.

Microsoft gives the limitation upto 4 virtual processor that use 4 cores from 1 physcal CPU.

Also I have that limitation can be increased more than 4.

Here is the link I found but it is not officially supported by Microsoft

Please correct I am understanding anything wrong.

Thanks for your help.
LVL 121
ID: 39620424
That is correct.

Author Closing Comment

ID: 39622493
Thanks for the clarifications

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