[Beowulf] Begginers question # 1

Mark Hahn hahn at mcmaster.ca
Mon Oct 4 18:44:49 PDT 2010


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.)

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