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Multiple single cores vs dual core vs quad core

Posted on 2009-02-13
Medium Priority
Last Modified: 2013-12-09
I am looking at putting together a server to use for testing.  I will be using VMWare's ESXi as the base.  My question is, when running several ( 8-12 ) virtual machines is it better to have 4 2ghz single core processors, 2 dual core 2ghz processors, or 1 quad core 2ghz processor, assuming FSB and cache are equal?
Question by:arstacey
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Expert Comment

by:Kyle Abrahams
ID: 23637700

Expert Comment

ID: 23637724
I anticipate running 8 VMs on my dual core processor with ESXi - currently I am running 4.

For simplicity I would suggest a single Quad Core Processor (especially if you are builidng your own "whitebox" server from components that are not "officially" supported - as the motherboard will be much cheaper that way).

It depends on if you are building your own partly or if you are buying a supported box through a vendor ... I assume that each VM will be single CPU and that nothing going to be taxing the system too heavily?

I built my ESXi server pretty cheap - around $600 I believe last year:

ASRock ALIVENF6G-VSTA AM2 NVidia 6100 Motherboard
AMD Athlon X2 BE-2400 Brisbane 2.3GHz
Intel Pro MT 1000 NIC
OCZ 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (x2)
Seagate Barracuda ES.2 ST3250310NS 250GB 7200 RPM SATA Hard Drive
SeaSonic S12 II SS-330GB ATX12V 330W Power Supply

My hardware is officially unsupported but I have had no issues running ESXi ...

Author Comment

ID: 23637829
I guess my real question is: are four single core, two dual core, and 1 quad core all equal in ability, assuming their cpu speed and cache are they same?
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Expert Comment

ID: 23638291

"The amount of performance gained by the use of a multicore processor depends on the problem being solved and the algorithms used, as well as their implementation in software (Amdahl's law). For so-called "embarrassingly parallel" problems, a dual-core processor with two cores at 2GHz may perform very nearly as quickly as a single core of 4GHz.[1] Other problems, though, may not yield so much speedup. This all assumes, however, that the software has been designed to take advantage of available parallelism. If it hasn't, there will not be any speedup at all. However, the processor will multitask better since it can run two programs at once, one on each core."

My answer in the case of ESX would be yes - because the hardware is "virtualized" in that it is being presented to the running VM's (who don't really know that they are being virtualized ...)

Author Comment

ID: 23638363
Thats not what I meant, or at least maybe we are just misunderstanding each other.   Does mashing four processing cores together to form a quad-core processor decrease the ability of each core?  If I am looking at two identical servers, one of which has four single core xeon processors and the other has a single quad core processor, assuming all other specs are the same, will one perform better than the other?

Accepted Solution

prickly earned 1000 total points
ID: 23638438
I think that this thread addresses your question: http://communities.vmware.com/thread/74399;jsessionid=76EB085D07FE72746C78694A56270FE0?tstart=0&start=0

RParker: "While the cores may require additional pathways, EACH core has it's own pathway to the memory. So the peformance of a quad core is actually FASTER than ANY dual core, even if they are separate.

Just because you have 2 sockets, does not imply 2 SEPARATE paths to memory, bus, and PCI. They still share the path.

Quad Core is much faster than Dual core, even in real world tests, and especially ESX. AMD is faster than Intel for pure memory operations, but that is another story.

But your numbers are off. A core isn't like hyperthreaded processors, not sure where you got that info, a core is a core, period. They are full processors.

That being said, that in this scenario yes a Dual Core (if they are separate sockets) is better than a single CPU quad core, because of the point of failure, but that would be the only reason.

Quad core is more expensive, but not by much. Quad core, even though slower per core, is more efficient. The overall speed you get is far and above that of dual core, 2 processors. "

Hope that this helps?

Author Comment

ID: 23638477
Thanks.  That is exactly what I was looking for!

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