[Beowulf] Southampton engineers a Raspberry Pi Supercomputer
Ellis H. Wilson III
ellis at cse.psu.edu
Wed Sep 12 09:02:42 PDT 2012
On 09/12/2012 11:42 AM, Vincent Diepeveen wrote:
> On Sep 12, 2012, at 5:24 PM, Lux, Jim (337C) wrote:
>> So, the question is... what's the smallest number of nodes in a
>> "demo/toy" cluster that gives you the "big iron" feeling. I'm
>> going to guess that 4 is too few.
I'd say even 16 would get you where you wanted to go, provided you get a
few smaller switches so the students can understand/run into network
topology problems (like why full bisection bandwidth really matters) as
well. If it's all on one switch networking will not really matter,
which it does a lot in "big iron."
> But most important: working with junk slow old hardware is not
> interesting to students. They want to be FASTER than their home PC.
> So give them a cluster where the software running on it is FASTER
> than their home PC.
> That's your first priority, or they wll be all total desinterested.
As someone who is still a student and who first put together his first
Beowulf cluster in 2008 made from "totally crap" PIII's that were in
some science building's attic of my University, and can speak from
experience that this vantage point is totally wrong. I was perfectly
excited overcoming the issues to get the 4 PIIIs I had to go 4x faster
than 1 PIII, since after all, you are going to run into very similar
infrastructure problems with a newer machine anyhow. I was just
learning the ropes about scalability then, learning how to code in MPI,
how to properly profile and monitor my system, how to install things in
parallel, etc -- I wasn't trying to set a flop record or anything. This
would be like taking a collegiate mechanical engineering class and
expecting kids to make a go-kart that was all-around better than their
car sitting back in their parking lot -- totally unrealistic.
In short, you've shared this negative, "if it's not faster then forget
about it" sentiment before Vincent, and it's neither constructive to the
conversation nor to be reasonably expected from Professors trying to run
a solid class on a budget. If I was the teacher, had a constrained
budget, and had the choice between 2 standard machines to share with the
whole class that WOULD go faster than the student's machines at home or
16 Raspberry Pi's that WOULDN'T go faster (for most workloads) than the
home computer, I would of course choose the latter.
When you are trying to educate people about cluster computing, the most
important thing is conveying the difficulties (both performance and
infrastructure related) working at scale -- not simply showing off that
the thing is "faster." Remember, students are paying CUSTOMERS for the
education; you should assume they are already interested in the concepts
and theory. It's not the educators job to spark this interest or feed
some flop-lust, but it is their job to expose as much of the theory and
pragmatics to the student as possible. This IS possible with MANY
slower machines, but ISN'T possible with FEW faster machines. If a few
students are being stubborn like you and want to drop the class because
the cluster isn't "fast enough," their loss.
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