[Beowulf] Infiniband modular switches
hahn at mcmaster.ca
Sun Jun 15 13:44:21 EDT 2008
> Static routing is the best approach if your pattern is known. In other
sure, but how often is the pattern actually known? I mean in general:
aren't most clusters used for multiple, shifting purposes?
> There are some vendors that uses only the 24 port switches to build very
> large scale clusters - 3000 nodes and above, without any
> oversubscription, and they find it more cost effective. Using single
so the switch fabric would be a 'leaf' layer with 12 up and 12 down,
and a top layer with 24 down, right? so 3000 nodes means 250 leaves
and 125 tops, 9000 total ports so 4500 cables.
> enclosures is easier, but the cables are not expensive and you can use
> the smaller components.
in federated networks, I think cables wind up being 15-20% of the network
price. for instance, if we take the simplest possible approach, and equip
this 3000-node cluster with a non-blocking federated fabric (assuming
just sdr) from colfax's current price list:
subtot unit n what
375000 125 3000 ib nic
117000 39 3000 1m host ib cables
148500 99 1500 8m leaf-top ib cables
900000 2400 375 24pt unman switch
1540500 total (cable 17%)
I'm still confused about IB pricing, since the street price of nics,
cables and switches are dramatically more expensive than colfax.
(to the paranoid, colfax would appear to be a mellanox shell company...)
for completeness, here's the same bom with "normal" public prices:
subtot unit n what
2100000 700 3000 ib nic
330000 110 3000 1m host ib cables
330000 220 1500 8m leaf-top ib cables
1500000 4000 375 24pt unman switch
4260000 total (cable 15%)
interestingly, if nodes were about 3700 apiece (about what you'd expect
for intel dual-socket quad-core 2G/core), the interconnect winds up being
28% of the cost.
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