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List:       beowulf
Subject:    Re: [Beowulf] Cluster Diagram of 500 PC
From:       Mark Hahn <hahn () mcmaster ! ca>
Date:       2007-07-11 16:18:10
Message-ID: Pine.LNX.4.64.0707111208290.31608 () coffee ! psychology ! mcmaster ! ca
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there are now several switches on the market that have,
for instance, 48x Gb ports and 2-4 10G ports.  having 
the higher-speed ports is attractive both to attach servers,
but also to build a larger switch fabric.  in particular, 
if you have 5x of these switches, you could plug their 10G
ports into each other and entirely avoid a top-level switch.
it "only" gets you to 240 nodes, but is also fairly cheap.

my question is: do switches these days have smart protocols for 
mapping and routing in such a configuration?  I know that the original 
spanning tree protocol would reduce such a config to a single tree,
turning off all the redundant links, effectively creating a hotspot
and ~doubling hop-counts.  maybe with vlans this could be avoided?

(incidentally, I notice HP is bragging about latencies <2.1 us
for 10G and <3.7 for 1G, as well as supporting jumbo packets 
even on fairly economy-level switches...)
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