Set IO striping

[jacwah]

Nek users on Lustre usually have to set the file striping on each output directory to get good IO performance, i.e. command lfs setstripe -c 1 .. We could make this more convenient for users by doing it automatically on a per-file basis where relevant. MPICH has builtin support for this using striping_factor key in an MPI_Info object. (Note that the MPICH_MPIIO_HINTS environment variable can still override these settings if necessary.)

Ref: https://www.alcf.anl.gov/files/CompPerfWorkshop_May2019_IOopt_harms.pdf

[steven-chien]

There could be a portability issue. For example, OMPI (that does not use ROMIO) has different hints on that: https://www.open-mpi.org/faq/?category=ompio#fs-parametesrs
A possible way is to make the code path a compile-time option with configure?

[jacwah]

Good point. It seems like the corresponding option for OMPI would be stripe_size. The simplest solution would be to just set both, it probably would not hurt to specify an Info option that is not used. For a more elegant solution, one could try to detect the MPI using some m4 magic as well.

[jacwah]

Discussed this with Philipp Schlatter in RT ticket 247964.