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Subject: [OMPI users] Multiple Subnet MPI Fail
From: Paul Monday (Parallel Scientific) (paul.monday_at_[hidden])
Date: 2010-11-22 09:28:56


We've been using OpenMPI in a switched environment with success, but
we've moved to a point to point environment to do some work. Some of
the nodes cannot talk directly to one another, sort of like this with
computers A,B, C with A having two ports:

A(1)(opensm)------>B
A(2)(opensm)------>C

B is not connected to C in any way.

When we try to run our OpenMPI program we are receiving:
At least one pair of MPI processes are unable to reach each other for
MPI communications. This means that no Open MPI device has indicated
that it can be used to communicate between these processes. This is
an error; Open MPI requires that all MPI processes be able to reach
each other. This error can sometimes be the result of forgetting to
specify the "self" BTL.

   Process 1 ([[1581,1],5]) is on host: pg-B
   Process 2 ([[1581,1],0]) is on host: pg-C
   BTLs attempted: openib self sm

Your MPI job is now going to abort; sorry.

I hope I'm not being overly naive but, is their a way to join the
subnets at the MPI layer? It seems like IP over IB would be too high up
the stack.

Paul Monday