two NICs - channel bonding - tradeoff

[Walter B. Ligon III]

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Now THIS is a really good question.  The answer is: no one can answer that
for you.  Someone should explore that idea to see.

Generally I think there are a number of interesting issues in using multiple
networks.  We have experimented with using one bus and one switched network
(back when switches were still pricey).

As you have correctly pointed out it will depend a lot on your application.
First off you need to find such an application.  Then do some experimenting
to see how best to use the network resources.

Of course, an alternative to using a dedicated network would be to modify
the networking code in the kernel to provide priority access to your special
traffic - of course getting switches to do that would be much more difficult.
This would make a great project for an MS student - mucking around in the
kernel to implement this.  I wonder if anyone know if the "out of band"
feature of TCP/IP (or is it UDP/IP?) actually gives priority to packets
at the network device queue, or if it simply provides a seperate buffer for
the socket?  One idea would be for the kernel to automatically route "out
of band" data via a different device.

Anyway, lots of issues to explore.  Please do, and then let us know what you
find.

Walt

> Assuming one has two 100MB NICs per node, is it
> always the best to channel bond? Or are there
> applications which run better with two separate
> communication channels.
> I could imagine an application where one has two
> kinds of messages. One kind is a short message but
> highly 'urgent'. Only after the message was delivered
> can the calculation continue. For example a
> synchronization message. And then another type of
> message which is higher in volume but is not
> time critical. So one channel would stay most of
> the time empty to provide the lowest latency for
> the urgent messages. Where the other channel is
> stuffed to transmit non-urgent data.
> 
> Do I gain something with running two separate 
> communication channels? Or do I fool myself?
> 
> Chris....

-- 
Dr. Walter B. Ligon III
Associate Professor
ECE Department
Clemson University