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Subject: Re: [OMPI users] a question about [MPI]IO on systems without network filesystem
From: Richard Treumann (treumann_at_[hidden])
Date: 2010-09-30 09:00:31


I will add to what Terry said by mentioning that the MPI implementation
has no awareness of ordinary POSIX or Fortran disk I/O routines. It
cannot help on those.

Any automated help the MPI implementation can provide would only apply to
MPI_File_xxx disk I/O. These are implemented by the MPI library.

It is possible for MPI-IO to be implemented in a way that lets a single
process or the set of process on a node act as the disk i/O agents for the
entire job but someone else will need to tell you if OpenMPI can do this,
I think OpenMPI built on the ROMIO MPI-IO implementation and based on my
outdated knowledge of ROMIO, I would be a bit surprised if it has his
option.

Dick Treumann - MPI Team
IBM Systems & Technology Group
Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
Tele (845) 433-7846 Fax (845) 433-8363

From:
Terry Frankcombe <terry_at_[hidden]>
To:
Open MPI Users <users_at_[hidden]>
Date:
09/29/2010 09:50 PM
Subject:
Re: [OMPI users] a question about [MPI]IO on systems without network
filesystem
Sent by:
users-bounces_at_[hidden]

Hi Paul

I think you should clarify whether you mean you want you application to
send all it's data back to a particular rank, which then does all IO (in
which case the answer is any MPI implementation can do this... it's a
matter of how you code the app), or if you want the application to know
nothing about it, but have the system somehow intercept all IO and make
it magically appear at a particular node (much harder).

On Wed, 2010-09-29 at 11:34 +0200, Paul Kapinos wrote:
> Dear OpenMPI developer,
>
> We have a question about the possibility to use MPI IO (and possible
> regular I/O) on clusters which does *not* have a common filesystem
> (network filesystem) on all nodes.
>
> A common filesystem is mainly NOT a hard precondition to use OpenMPI:
>
http://www.open-mpi.org/faq/?category=running#do-i-need-a-common-filesystem

>
>
> Say, we have a (diskless? equipped with very small disks?) cluster, on
> which only one node have access to a filesystem.
>
> Is it possible to configure/run OpenMPI in a such way, that only _one_
> process (e.g. master) performs real disk I/O, and other processes sends
> the data to the master which works as an agent?
>
> Of course this would impacts the performance, because all data must be
> send over network, and the master may became a bottleneck. But is such
> scenario - IO of all processes bundled to one process - practicable at
all?
>
>
> Best wishes
> Paul
>
>
>
> _______________________________________________
> users mailing list
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users

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