Thanks for the quick response ... I've been thinking about this today and tried a few things on my CentOS mini connected cluster ...

To use tcp btl I will have to set up a bridge on A with ib0 and ib1 participating in the bridge, then tcp btl could be used as you suggest.  Unfortunately, the obvious solution to use bridge-utils on CentOS does not support Infiniband adapters.

This is now straying out of MPI range to a networking issue ... any ideas would be greatly appreciated on bridging at the IP over IB tier in a cluster.  This must be a solved problem but I'm not having a lot of luck with google and the archives.

Paul Monday



On Nov 22, 2010, at 7:46 AM, Terry Dontje wrote:

You're gonna have to use a protocol that can route through a machine, OFED User Verbs (ie openib) does not do this.  The only way I know of to do this via OMPI is with the tcp btl.

--td

On 11/22/2010 09:28 AM, Paul Monday (Parallel Scientific) wrote:
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
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Terry D. Dontje | Principal Software Engineer
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Oracle - Performance Technologies
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