[Beowulf] torus versus (fat) tree topologies
joachim at ccrl-nece.de
Mon Nov 8 12:50:49 PST 2004
Chris Sideroff wrote:
> My investigation thus far has led me to believe that one reason a torus
> topology might be better is because it eliminates the need for a switch.
> On the other hand fat tree interconnects seem to dominate the
> larger(est) clusters out there, why?
> I'm looking more for comments about implementation and maintenance
Torus topologies are easier to scale as cost and effort scale linearly
with the number of nodes. And there wer and are some very
popular/well-performing machines using this topology (Intel Paragon/ASCI
Red, Cray T3D/E, and now BlueGene). In the cluster range, you can use
SCI ('Wulfkit') for this.
FatTree topology gives better (theoretically full) bisection bandwidth,
and examples like Quadrics and Myrinet show that this can be done in a
(more or less) cost-effective way.
Manageability of a fattree network should be easier, as a failing node
does not affect message routing at all. Which doesn't mean that the
difference in complexity concerning this is necessarily experienced by
the user or administrator if the management software is well implement.
Not to forget that other topologies do exist, too (EarthSimulator/NEC SX
use a full single-stage crossbar).
Joachim Worringen - NEC C&C research lab St.Augustin
fon +49-2241-9252.20 - fax .99 - http://www.ccrl-nece.de
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