[Beowulf] noobs: what comes next?

Mark Hahn hahn at mcmaster.ca
Mon Jun 22 17:16:06 PDT 2009

> different, and I would like to follow the general rule of newbish
> clustering: use homogeneous nodes.

I wonder where that rule came from.  homogeneity is certainly more 
convenient, and might actually make sense for certain domains (where
some amount of global synchrony is required.)  but for a starter cluster,
heck no!  for CFD, you simply decompose your work to match the speed
of your nodes - you don't need to assume each node is equally fast,
or that each piece of work takes the same effort...

> Second problem is that I can get miniITX motherboard for 89$. That's the

there's nothing wrong with the form-factor - the problem is that atom 
processors are not built for speed.

> optimal price. I'm worried about the power consumption of regular pc's,
> and the power needed for miniITX is really low (90 wats for the
> motherboard and CPU included).

that would be a strange miniitx/atom system if it dissipated that much - 
I think my media server is more like 30W full-on.  the atom approach, 
while amusing, starts out with so many disadvantages.  it's slow, with a 
small cache and slow memory system.  OK, you could still do OK if you 
use enough of them.  but "enough" will mean extra infrastructure per node
(gpu/northbridge, random MB devices, all of which dissipate more than 
the CPU).  not to mention the fact that no task that is meaningfully
"parallel" scales perfectly: with lots of slow processors, you really want
to take an approach like sicortex (rip?) who provided a very nice network
as well as great packaging.

> The third issue is that I'm not just using this cluster for learning. At
> the end, it would be amazing to be able to run about 500 000 control
> volume CFD cases used so far (ship hydrodynamics simulations - movement
> of the ship excluded) for about 6 days worth of 20 seconds physical time
> on a cluster that's easily moved and uses regular PC's PSU (cheap on
> electricity).

I think you're making some strange assumptions about speed:power ratios.
a 65W quad-core mainstream processor will be a joy to use compared to 
a heap of atoms, even if you completely ignore the overhead of the 
support electronics.  for PSUs, you simply want to do two things:
size it so you're running at ~85% capacity, and get a plus80 model (gold, etc).

>    For scaling info: I've ran 175 000 FV cells on my dual core laptop
> (HP compaq dual core 1.73 Ghz) for 6 days to get 4 seconds physical
> time. Does this sum up to a cluster being about 14 times faster machine
> than my laptop? I would be satisfied with much less. :)

scaling is always a struggle: you want fairly significant cpus,
unless you can specifically provide low-overhead infrastructure
(support chips, networking - basically "custom").

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