...
Users have to typically start with the default configuration and try couple of PIO_NUMTASKS and PIO_STRIDE options to get an optimal PIO layout for a model configuration on a particular machine. On large machines, empirically we have found that we need to constrain the number of PIO I/O tasks (PIO_NUMTASKS) to less than 128 to prevent out of memory errors.
Examples:
For small core counts, it's usually most efficient to run all the processes sequentially with all processes using all available cores (though if one process scales poorly it may make sense to have it run on fewer processors while the remaining processors idle). Here is an example of a serial PE layout:
...