1. Open MPI MPI_File_* API functions, constants, handles ROMIO plugin All the other MPI_* API functions, constants, handles How it normally looks (v1.6)

2. Open MPI MPI_File_* API functions, constants, handles ROMIO plugin OMPIO plugin All the other MPI_* API functions, constants, handles How it normally looks (v1.7)

3. Open MPI MPI_File_* API functions, constants, handles ROMIO plugin All the other MPI_* API functions, constants, handles --disable-mpi-io (v1.6) Compile/link time error if you call MPI_File_open() because that symbol doesn’t exist in mpi.h or libmpi.

4. Open MPI MPI_File_* API functions, constants, handles ROMIO plugin All the other MPI_* API functions, constants, handles --disable-mpi-io (v1.7) OMPIO plugin

5. Open MPI MPI_File_* API functions, constants, handles ROMIO plugin All the other MPI_* API functions, constants, handles --disable-io-romio (v1.6) Run-time error if you call MPI_File_open() because OMPI has no plugin to do the MPI I/O functionality.

6. Open MPI MPI_File_* API functions, constants, handles ROMIO plugin All the other MPI_* API functions, constants, handles --disable-io-romio (v1.7) OMPIO plugin No run-time error if you call MPI_File_open() because OMPI will use the OMPIO plugin