[mpas-developers] Parallel I/O

Michael Duda duda at ucar.edu
Thu Dec 1 10:45:24 MST 2011

Hi, All.

I've been working on a branch of the repository to make use of the PIO
library -- the same library used in CESM -- to write history and restart
files from MPAS. The branch should now be in a working state for all
cores, with one major exception: restartability. Since PIO doesn't
handle character-typed data, which we use for writing the time
coordinate information as the xtime variable. In the branch, I've simply
disabled writing of the xtime variable, with the consequence that
restarting may not quite work -- I've not yet tested it, so it could be
a simple matter for now of commenting out the date-checking code when
reading a restart file. I'll send out a separate e-mail soon about the
issue of time coordinate information in our input and output files.

If anyone would like to try out the branch, I'll be glad to offer help
in compiling and running. To compile, the pNetCDF library will first
need to be installed, followed by a compile of the PIO library. With
these libraries available, one only needs to set the environment
variable PNETCDF to point to the pNetCDF installation and the PIO
environment variable to point to the top-level PIO directory.

When running, there are two additional namelist variables to specify in
the &io namelist record. config_pio_num_iotasks specifies the number of
MPI tasks to use for writing to the file, and config_pio_stride is the
stride between I/O tasks.

Again, if there are any questions, I'll be glad to assist!


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