[Beowulf] Network considerations for new generation cheap beowulfcluster

[Jim Lux]

At 09:19 AM 5/22/2007, Peter St. John wrote:
>A hypercube 
>(<http://en.wikipedia.org/wiki/Hypercube>http://en.wikipedia.org/wiki/Hypercube) 
>also gets you exponential space; the max hops is the dimension (3 
>for a 3-dimensional cube) and the number of nodes is exp(base 2) of 
>the dimension (8 vertices on a cube). To do a tesseract (4-cube), 
>which looks like two cubes nested, you'd need 4 ports per node, 16 
>nodes, 32 cables, max hop 4. I've poked around and don't see a great 
>4 ports per node solution; I like the suggestion of putting a router 
>on a motherboard.

Mind you, this is what Intel started with on their iPSC/1 and iPSC/2 
computers.  The early ones had multiple NICs in the nodes, then, 
later, they had a 8 port (I think) router in each node.

It's not clear that this saves anything over a simpler architecture 
(e.g. external switch with lots of ports in a crossbar) unless you 
can do circuit switched routing (so you don't have a one packet delay 
in the switch) AND your algorithm can take advantage of it. I spent 
quite some time in the late 80s trying to figure out clever ways to 
take advantage of a hypercube topology for a modeling 
application..  I'm sure there are algorithms which are a natural fit, 
but the ones I was using weren't.



James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875 
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