Beowulf Questions

[Donald Becker]

On Fri, 3 Jan 2003, Randall Jouett wrote:
> Donald Becker wrote:
> >     It transparently uses all available cluster nodes, and works even if
> >      that number is '0'.
> 
> I like this.

Our cluster philosophy is that the end user should not be required to
do anything new or special to run a cluster application.

That means
   Applications should work even if there is only a single machine in
   the cluster.  Many beginner MPI applications don't handle this case
   correctly.

   Cluster applications should not require a helper program such as
   'mpirun' or 'mpiexec'.

   The application code should interact with the scheduler to set any
   special scheduling requirements or suggestions.

A sophisticated user should still be able to optimize and do clever
things, but the basic operation shouldn't require any new knowledge.

> >     It does all of the serial setup and run-time I/O on the front end
> >       machine (technically, the MPI rank 0 node).  This minimizes
> >       overall work and keeps the POV-Ray call-out semantics unchanged
> >     It does the rendering only on compute nodes (except for the N=0 case). 
> >     It completes the rendering even with crashed or slow nodes.
> 
> Ah. So it redistributes the work, huh? Kewl.

Here we use knowledge about the application semantics to implement
failure tolerence.  When we have idle workers and the rendering isn't
finished, we send some of the remaining work to the idle machine.
If a machine fails we still finish the rendering and do the final
call-outs, but don't cleanly terminate.


-- 
Donald Becker				becker at scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993