As Rob mentions There are three capabilities to consider:
1) The process (or processes) that will do the I/O are members of the file handle's hidden communicator and the call is collective 2)) The process (or processes) that will do the I/O are members of the file handle's hidden communicator but the call is non-collective and made by a remote rank 3) The process (or processes) that will do the I/O are not members. The MPI_COMM_SELF mention would probably be this second case. Number 2 & 3 are harder but still an implementation option. The standard does not require or prohibit them. 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: Rob Latham <r...@mcs.anl.gov> To: Open MPI Users <us...@open-mpi.org> List-Post: users@lists.open-mpi.org Date: 10/19/2010 02:47 PM Subject: Re: [OMPI users] a question about [MPI]IO on systems without network filesystem Sent by: users-boun...@open-mpi.org On Thu, Sep 30, 2010 at 09:00:31AM -0400, Richard Treumann wrote: > 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 outdated knowledge of ROMIO, I would be a bit surprised if it has his 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. SURPRISE!!! ROMIO has been able to do this since about 2002 (It was my first ROMIO project when I came to Argonne). now, if you do independent i/o or you do i/o on comm_self, then ROMIO can't really do anything for you. But... - if you use collective I/O - and you set the "cb_config_list" to contain the machine name of the one node with a disk (or if everyone has a disk, pick one to be the master) - and you set "romio_no_indep_rw" to "enable" then two things will happen. first, ROMIO will enter "deferred open" mode, meaning only the designated I/O aggregators will open the file. second, your collective MPI_File_*_all calls will all go through the one node you gave in the cb_config_list. Try it and if it does/doesn't work, I'd like to hear. ==rob -- Rob Latham Mathematics and Computer Science Division Argonne National Lab, IL USA _______________________________________________ users mailing list us...@open-mpi.org http://www.open-mpi.org/mailman/listinfo.cgi/users
