[Beowulf] Cluster newbie, power recommendations

Robert G. Brown rgb at phy.duke.edu
Mon Mar 20 15:50:45 PST 2006

On Sun, 19 Mar 2006, Eric Geater at Home wrote:

> Howdy, everyone!
> Maybe this is a question better suited for hardware heads, but I've become
> Beowulf curious, and am interested in learning a hardware question.
> I have access to a bunch of old ATX computers.  The most likely common
> processor will no doubt be Pentium II 400, with hard drive space around 10gb
> each.  If I part out all the RAM from candidate boxes, I might be able to
> max them out at 384mb RAM.  But the underlying fact that drives me to this
> curious point is that they're all free, and thus candidates for
> experimentation.
> My greatest question, though, revolves around power distribution.  It seems
> kinda weak to simply use one PSU per motherboard, especially if I take the
> time to devise a cabinet in which to operate the goodies.  Is it possible to
> run maybe two or three motherboards off a single power supply, given that
> the amount of known power committed to run a mobo is light, compared to the
> total workload of the average 350w PSU?
> This is a power-saving concept... if I could run 16 mobo's on 8 (or even 6)
> power supplies, it might be more beneficial to my health and well-being when
> the electric bill comes in.

Sigh.  If you do the math, you are better off buying a single AMD64 than
using the whole cluster for "work", especially as far as power is
concerned.  16 mobos is likely close to 1600 watts -- almost certainly
over 1000 watts even if you use larger/collective power supplies.
Compare that to the 100-200 watts for a single AMD64, and you're looking
at an ~$800/year difference in cost paying for the electricity and
cooling alone (at an estimated $1/watt/year, which is a bit high
depending on where you live but probably not even a factor of two high).

The AMD64 is probably not QUITE the aggregate speed available to 16 400
MHz PII's, but you could afford a second one AND the power (or a dual
core one) and save yourself hundreds of dollars overall for the same
amount of power.

So your cluster is not an economical proposition for nearly any kind of
real work -- you can get more done cheaper in other ways. HOWEVER, most
people who build this kind of cluster do so for the fun and experience,
not the work.  If this describes you, then I'd suggest not worrying too
much about the power saving right away -- somebody on this list (I can
think of a couple of folks offhand:-) will likely suggest SOME ways of
doing collective power, and there used to be a really nice shelved
cluster on the web that used a single beefy power supply and special
connectors per shelf of something like 4 motherboards.  Google harder --
hopefully it is still there (or check the list archives to see if you
can find a reference, this was a year plus ago).  When they do or you
figure it out, you can try scaling your cluster up or laying out the
motherboards naked on a frame.  In the meantime, a cluster of nice neat
towers is pretty lovely...


> Thanks, and I'll take any suggestions you might have.  Google has not been
> friendly to me in this search.
> Eric Geater
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Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu

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