VM Odd CPU's and large memory


I'm confused, I've started this new role and they've assigned 3 cores and 10GB of memory to a VM, I cannot fathom why you would assign it in this fashion. Would this cause issues for the OS trying to manage the odd number of cores and the excessive amount of memory.

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Alex GreenProject Systems EngineerAsked:
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Did not heard or aware with any issues with odd configuration

Ideally cores should be in multiples of 2 and memory also in multiples of 4

May be team knows exact resource requirement and they are trying to save resources which can be utilized elsewhere
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
BONKERS and they do not know what they are doing!!!
nociSoftware EngineerCommented:
Why would odd be a problem... (3core CPU's are sold, those are actually 4+ core CPU's with 3 working CPU's on die, so in stead of throwing it into the bin, they sell it for lower prices).
The critical boundary for CPU's is 1 or many.   with 1 no need for special constructs (aka spinlocks) tocoordinate stuff with neighbours. With 2 or 2000 you do need them.
Also adding more CPU's also adds more overhead into those spinlocks.  (1st extra CPU will add 99.98% capacity (not 100%) the 1000'th cpy might only add 70% more capacity (very depending on workload though).  
In general data (IO intensive) moving systems are more happy with less CPU's , Compute (usermode compute) are more happy with many CPU's....

Oracle for instance calculates License fees on # of cores, so one more core might be a investment of a few hunderds of K$.
(And if not careful you also need OVM as product otherwise you need to pay for all cores in the hardware.)
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Alex GreenProject Systems EngineerAuthor Commented:

I understand that, but can you please tell me what affect this would have on the server in the first place, saying it's bonkers (which I agree with) isn't really justification in telling them they are doing it wrong.

Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Remove the 3rd, or add another and check the metrics.

do they need more than a single vCPU ?
Alex GreenProject Systems EngineerAuthor Commented:
Yeah, it's a print server, it's currently utilizing 80% - 100% on all 3. Still trying to figure out what's causing it. It's secure print so requires a little more.

When you say check the metrics, what do you mean? The ones within V-Center, the ones on the host or the ones within windows?
nociSoftware EngineerCommented:
80%-100%  on all three sound like right sized to demand.  Any system using less than 70% CPU is wasting part of the energy put into it for no use.   continuous on 100% could mean there is insufficient capacity.
between 80-100 and no complaints about slowness then 3 seems to be the right amount here.

How about memory, here the peakload also needs to be runable. (and probably without danger of swapping...).
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Have a read of this articles, and links, and you'll find the bottlenecks...

HOW TO:  Performance Monitor vSphere 4.x or 5.0

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Philip ElderTechnical Architect - HA/Compute/StorageCommented:
Is this a VMware or Hyper-V setup?

Why would an odd number of vCPUs be a problem on VMware? It would not on Hyper-V as a vCPU = Thread to the CPU with the three being scheduled and processed through the CPU pipeline without any issue that I can see?

I have two very thorough EE articles on all things Hyper-V that may help to answer some questions:

Some Hyper-V Hardware and Software Best Practices
Practical Hyper-V Performance Expectations
Alex GreenProject Systems EngineerAuthor Commented:

THanks andrew, I'll take a look.


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