[Beowulf] if you had 2 switches and a bunch of cable, what would you do?

Paul Johnson pauljohn32 at gmail.com
Sun Dec 20 12:59:08 PST 2009

I inherited a few big racks of unused Dell PowerEdge servers.  There
are 2 1GB switches in each rack, and each node in the cluster has at
least two ethernet connections.

I have a head node and some compute nodes up and running in Rocks
Cluster 5.2, but in my haste to see that the hardware actually works,
I've only only cut and patched enough cables to use one switch for the
internal network.

What to do with the other switch? As far as I understand it, I have 2
options (aside from selling the extra switch on Ebay :))

Option 1. Create 2 separate internal networks. In wiring drawings for
clusters, I often see one administrative network and one for
computations (mpi, and so forth).

The downside for that is that I don't yet understand how user programs
are supposed to differentiate the 2 internal networks and send
messages through the computation network. I've not had the luxury of 2
ethernet cards before.

Option 2. Try "channel bonding" to try to increase the throughput on a
single ethernet node.  That has some appeal because the users just see
one network.

I'm not aiming for the "high availability" approach of using the
second switch as a fallback.  Rather, I'm aiming for the fastest &
widest connection possible in and out of each compute node.

My head node still has just one 1GB ethernet connection going into it,
and if I could believe that channel bonding would actually improve
throughput, I suppose I could get another line (or even 2 more) going
into the head node.  The headnode has 4 ethernet jacks, so I suppose I
could double up inside and outside.

I'd be glad to hear your thoughts.

Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas

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