A site administrator with knowledge of the storage and networking capabilities of a machine might be able to come up with a set of hint values that work better for that machine than the ROMIO default values. As an extention to the standard, ROMIO will consult a ``hints file''. This file provides an additional mechanism for setting MPI-IO hints, albeit in a ROMIO-specific manner. The hints file contains a list of hints and their values. ROMIO will use these initial hint settings, though programs are free to override any of them.
The format of the hints file is a list of hints and their values, one per line. A # character in the first column indicates a comment, and ROMIO will ignore the entire line. Here's an example:
# this is a comment describing the following setting cb_nodes 32 # these nodes happen to have the best connection to storage cb_config_list n01,n11,n21,n31,n41
ROMIO will look for these hints in the file /etc/romio-hints. A user can set the environment variable ROMIO_HINTS to the name of a file which ROMIO will use instead.