[Beowulf] Begginers question # 1

Glen Beane Glen.Beane at jax.org
Tue Oct 5 06:54:47 PDT 2010

On Oct 4, 2010, at 9:44 PM, Mark Hahn wrote:

> no.  it's the application that counts.
>> If I build a cluster with 8 motherboards with 1 single core each would it
>> be the same as using just one motherboard but with two quad core
>> processors?
> of course not.  communication among cores on a single board
> will certainly be faster than inter-board communication. 
> it's the application that matters: how frequently do threads/ranks 
> of the application communicate?  are messages small or large? 
> can the app's communication be formulated as mostly-read sharing of data? 
> these are all very much properties of the application, 
> and they determine how suitable any particular hardware will be.
>> I wanna build one of these but wanna save money and space and
>> if what counts is the amount of cores to process info I think fewer
>> motherboards with dual six-core processors is definitely cheaper just
>> because I wont be needing that many mothers power supplies etc. thanks
> power supplies aren't your main concern, since good ones are about 93%
> efficient.  but going with more-core systems is, in general, a good idea.
> mainly for amortization reasons: probably fewer disks, extraneous sutff
> like video interfaces, fewer parts to fail, fewer systems to administer, etc.
> there can be disadvantages to more-core systems too, since some of the parts
> being shared (amortized) may be performance bottlenecks.
> the sweet spots depends on what systems are in volume production - 
> right now, 2-socket systems are the right building block in most cases.
> 4-socket systems would be attractive, but they tend to ship in so much 
> lower volume that their price is nonlinearly high.  1-socket servers 
> tend to cost more than half a 2-socket (where "server" means at least 
> "has ECC memory" - that is, not a desktop.)

the price point of the 4-socket Magny Cours systems are pretty attractive.  Now that AMD did away with having to pay a premium for CPUs that were compatible with quad socket systems I think you can get more cores for the same amount of money by going quad socket Magny Cours.   I purchased a small cluster mid summer, and went with 4-socket 32 core nodes. 

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