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assigning vcpus vmware

Posted on 2014-01-22
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Last Modified: 2016-04-30
When assigning vcpus, should you am to match the sockets and the cores?

i.e.

If i have a physical server with 2 physical sockets, each having 6 cores.  If you wanted to assign your vm 4 vcpus., would u assign

4 x virtual sockets

or

2 x virtual sockets with 2 cores per socket
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Question by:cmatchett
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LVL 7

Expert Comment

by:Ned Ramsay
ID: 39800961
It makes no difference to performance.

However some software is licensed per "socket" so it would be cheaper to have 1 socket with 6 cores than 2 sockets with 3 cores.

Hope that helps.
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LVL 117
ID: 39801011
Assign sockets - normally.

If you have license restrictions assign cores.

So I would assign

2 vCPU - Test

add another

2 vCPU - Test

Any difference to performance, either stick or decrease back to 2 vCPU.

Too many processors could slow a VM down, and make performance worse.
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Author Comment

by:cmatchett
ID: 39801165
maybe i should ask this in a different question.  i am trying to use the exchange calculator to give me exacts.

so there are 2 mbx servers that are in a dag and are multi-roled.  enterprise vault is being used, as is BES.  AV is also running on these servers as is mail ex-claimer.

2000 users.
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Expert Comment

by:Ned Ramsay
ID: 39801194
Every setup is different, 4 sockets vs 4 cores makes no difference AT ALL to performance.
If you have been recommended 4vCPU for your sizing then use that.

What Andrew is warning about is that if you set too many vCPUs to a VM and they are busy processing on another VM then it waits for them to become free all at once which has a detrimental effect on your infrastructure.

I would recommend running it with say 2 or 3 vCPU first and then expand as required. Unfortuantely there is no "one size fits all" guide for VMs as each case is different.

But to answer your original question VMWare only has the Socket vs Core option to take into account licensing for applications that run on the VMs.
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Author Comment

by:cmatchett
ID: 39801280
these particular servers are currently maxed out at 100% with 4 vcpus

we want to now size it properly.  so we would have to raise a change to get another vcpu just allow us to run the profile analyzer...
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Expert Comment

by:Ned Ramsay
ID: 39801285
Yes if you do not have full control over your VMware environment you will need to get extra added and re-run the analyser.

As a side note I recommend reading this: http://www.vmware.com/files/pdf/exchange-2010-on-vmware-design-and-sizing-examples.pdf

Let me know if I can be of more help.

Edited: Andrew Hancock
VMware Zone Advisor
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Author Comment

by:cmatchett
ID: 39801294
we were just going to request an extra vcpu for the analyzer.  I will get asked a question as why only 1 - will that allow you to run it they will say without impacting the service.  a service interruption wouldn't be accepted and then i guess it will fall at my feet.  its quite flakey as it maxed out
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Author Comment

by:cmatchett
ID: 39801303
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Expert Comment

by:Ned Ramsay
ID: 39801379
Ok unfortunately you may need to add 2 more CPU and see then but it's something you can't test until they are in place.
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Author Comment

by:cmatchett
ID: 39847040
servers have been profiled.

exchange calculator recommends 8 vcpus and 24 GB of RAM be assigned to each vm
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LVL 117
ID: 39847088
Thats alot of vCPUs.

I would try increasing to 4 vCPU (sockets)
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Author Comment

by:cmatchett
ID: 39847743
each server currently has 5 vCPUs

of the 8 processor cores assigned, 6 cores will be utilized and the processor Utilization will be 56% on single server failure.  The target is 40%.

These physical servers are 2/3 years old
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LVL 117
ID: 39847780
Okay, add another 3 vCPUs.
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Author Comment

by:cmatchett
ID: 39885269
sorry for not getting back to this, this is till on going
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Accepted Solution

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cmatchett earned 0 total points
ID: 41564503
coming back to close this one off - sorry for the delay.

We ended up scaling out the exchange virtual machines, each Exchange VM has 1 socket with 6 cores each.  The vmware guys said that assigning 6 vcpus to each of the exchange vms will ensure that the exchange vm fits within the numa node.  They said that this will offer the best performance.

Thanks for all your direction.
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LVL 117
ID: 41564536
Seems in contradiction to their blog.

Sockets should be used instead of Cores for best performance.

Recommended Practices

#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.

#2 When you must change the cores per socket though, commonly due to licensing constraints, ensure you mirror physical server’s NUMA topology. This is because when a virtual machine is no longer configured by default as “wide” and “flat,” vNUMA will not automatically pick the best NUMA configuration based on the physical server, but will instead honor your configuration – right or wrong – potentially leading to a topology mismatch that does affect performance.


Source
Does corespersocket Affect Performance?
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Author Comment

by:cmatchett
ID: 41564574
0
 
LVL 117
ID: 41564596
It still states the same Sockets (vCPUs, CPUs) not Cores,

that document still states use Sockets, e.g. vCPUs, not Cores.

So what did you assign 1 vCPU x 6 Cores ?
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Author Comment

by:cmatchett
ID: 41564648
In Windows it says 1 CPU and has 6 cores?

I could have the terminology mixed up.  

they said that because each server has 2 physical sockets, each having 6 cores, keeping the number of vCPUs to 6 or under would ensure that that it would stay within the same NUMA node?

The exchange calculator said that each exchange vm required 8 vCPUs each.  This is why we scaled out the exchange environment.
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LVL 117
ID: 41564667
So in the end, you assigned 6 vCPU x 1 Core ?

instead of assigning 1 vCPU x 6 Cores ?
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Author Comment

by:cmatchett
ID: 41564795
I will get to grips with the vmware terminology one day :)

The terminology on the exchange calculator is: processor cores / server.

on the processor query tool it says: Enter the number of virtual processors to be allocated to each server.  I have a value of 6 in the processor query tool and also in the exchange calculator.

In task manager, Each exchange vm has 1 socket 6 cores.
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Author Closing Comment

by:cmatchett
ID: 41572352
this is what we ended up going with
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