[Beowulf] using two separate networks for different data streams

Douglas Eadline deadline at clustermonkey.net
Fri Jan 27 12:11:13 EST 2006


>>   I've seen architectures with two network switchs, one is used for I/O
>> (writing, reading, so on) and another for message passing (MPI). how is
>> this achieved? I get the idea, from one place, where the applications
>> running must be aware of this but I was thinking that for this to work
>> it
>> must be transparent to the application. How can this be achieved?
>
> in short: you assign a different IP to each interface (as normal).
> it's convenient to use one non-low-order in the IP to distinguish,
> and also nice to have separate hostnames like node1 and node1-mpi.
>
> I wonder whether anyone has critically evaluated whether this is
> important.
> cluster people I talk to like to say fuzzy things like "separate networks
> make the cluster breathe better".
>
> as much as I admire car analogies, I observe that when apps are doing IO,
> they tend not to be doing MPI.  if your workload is like that, bonding
> rather than partitioning would actually improve performance.  I wonder
> whether the partitioning approach might actual reflect other constraints,
> such as using half-duplex hubs, or low-bisection networks.



Indeed, an excellent question. It seems logical, does it really help though
(or do I just feel clever about using the extra Ethernet Port)  I can see
that if you have a lot of monitoring traffic that might cause an issue,
but I have never tested that notion as well. Of course it all depends...
I wonder if a dual Ethernet node would be better served by something like
a FNN (http://aggregate.org/FNN/) Tim Mattox can probably weigh in on
this.

--
Doug

>
hahn> regards, mark hahn.
>
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-- 
Doug
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