Thanks Gilles, this is the solution. I will set OMPI_MCA_io=^ompio automatically when loading the parallel hdf5 module on the cluster.
I was tracking this problem for several weeks but not looking in the right direction (testing NFS server I/O, network bandwidth.....) I think we will now move definitively to modern OpenMPI implementations. Patrick Le 03/12/2020 à 09:06, Gilles Gouaillardet via users a écrit : > Patrick, > > > In recent Open MPI releases, the default component for MPI-IO is ompio > (and no more romio) > > unless the file is on a Lustre filesystem. > > > You can force romio with > > mpirun --mca io ^ompio ... > > > Cheers, > > > Gilles > > On 12/3/2020 4:20 PM, Patrick Bégou via users wrote: >> Hi, >> >> I'm using an old (but required by the codes) version of hdf5 (1.8.12) in >> parallel mode in 2 fortran applications. It relies on MPI/IO. The >> storage is NFS mounted on the nodes of a small cluster. >> >> With OpenMPI 1.7 it runs fine but using modern OpenMPI 3.1 or 4.0.5 the >> I/Os are 10x to 100x slower. Are there fundamentals changes in MPI/IO >> for these new releases of OpenMPI and a solution to get back to the IO >> performances with this parallel HDF5 release ? >> >> Thanks for your advices >> >> Patrick >>
