Re: mainboard-power source for GPU

From: Axel Kohlmeyer (akohlmey_at_gmail.com)
Date: Tue Jan 25 2011 - 06:36:57 CST

On Tue, Jan 25, 2011 at 2:47 AM, Francesco Pietra <chiendarret_at_gmail.com> wrote:
> Hello:
>
> May I ask which mainboard and power source proved to work for FOUR
> GTX470 and CUDA NAMD? My plan is to assemble the computer, not to buy
> a ready-to-use one. Should GTX470 be a particular brand?

there is a big difference between "work" and "work well".
one problem is the _combined_ PCIe bandwidth. many
boards that have more than 2 PCIe-x16 slots don't have
more PCIe bandwidth than with 2 slots and thus using more
than two GPUs may not give you the speedup that you expect.
you will need two CPUs and two southbridges for the maximum
PCIe bandwidth. you also have to worry about the case and
cooling. four high-end GPUs will produce a _significant_
amount of heat (~1kW) under full load. that has to be
removed from the case. most "desktop" cases are not
fit for that.

> I would also be interested to put more CPUs than needed (with two
> sockets for multicores), in view to alternatively use the machine also
> for electronic calculations. Therefore, slots enough than required by
> single-precision MD.

if you want to have multple processors you have to use a server
style mainboard and then you are best off with buying a complete
case with mainboard combo right away and then the savings of
assembling parts by yourself are small and the risk of damages
to parts (e.g. the CPUs) by assembling the machine by yourself high.

i have not tried much else, so i don't know if there is something
better available, but i have made good experiences with supermicro
4-GPU chassis'. they come in cases that can be either used as
workstation or rackmounted and you can control the case fan
settings from the BIOS. with 4 fermi class GPUs that kind of
machine produces a significant amount of heat and noise though
(i had one for a few weeks in my office).

if you are after saving money over everything else, buy a gaming,
single processor mainboard and stick to two GPUs (or three with
some performance degradation). remember that "you get what you
pay for", i.e. there is some value associated to "workstation" type
hardware in that it is more reliable and better suited to 24/7 operation.
this becomes all the more important depending on what kind of
environment you are going to place the machine in.

cheers,
     axel.

> I am based in W Europe.
>
> thanks
>
> francesco pietra
>
>

-- 
Dr. Axel Kohlmeyer
akohlmey_at_gmail.com  http://goo.gl/1wk0
Institute for Computational Molecular Science
Temple University, Philadelphia PA, USA.

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