this is in theory still correct, the default MPI I/O library used by Open MPI on Lustre file systems is ROMIO in all release versions. That being said, ompio does have support for Lustre as well starting from the 2.1 series, so you can use that as well. The main reason that we did not switch to ompio for Lustre as the default MPI I/O library is a performance issue that can arise under certain circumstances.
Which version of Open MPI are you using? There was a bug fix in the Open MPI to ROMIO integration layer sometime in the 4.0 series that fixed a datatype problem, which caused some problems in the HDF5 tests. You might be hitting that problem. Thanks Edgar -----Original Message----- From: users <users-boun...@lists.open-mpi.org> On Behalf Of Mark Dixon via users Sent: Monday, November 16, 2020 4:32 AM To: users@lists.open-mpi.org Cc: Mark Dixon <mark.c.di...@durham.ac.uk> Subject: [OMPI users] MPI-IO on Lustre - OMPIO or ROMIO? Hi all, I'm confused about how openmpi supports mpi-io on Lustre these days, and am hoping that someone can help. Back in the openmpi 2.0.0 release notes, it said that OMPIO is the default MPI-IO implementation on everything apart from Lustre, where ROMIO is used. Those release notes are pretty old, but it still appears to be true. However, I cannot get HDF5 1.10.7 to pass its MPI-IO tests unless I tell openmpi to use OMPIO (OMPI_MCA_io=ompio) and tell UCX not to print warning messages (UCX_LOG_LEVEL=ERROR). Can I just check: are we still supposed to be using ROMIO? Thanks, Mark
