The Weather Research Forecast (WRF) model developed at NCAR is the community weather model. WRF is designed in such a way that it has standard configuration and IO common APIs to enable external IO packages to be easily added to. An application can select which IO module to use. The current WRF software package supports a netCDF WRF IO module. This talk presents a new HDF5 WRF IO modules, The Parallel HDF5-WRF uses the parallel HDF5 library, which is implemented with MPI IO. Performance studies show that this module can improve performance for computations with large IO requirements. The sequential HDF-WRF module can support in memory compression that can save disk space.

1. An HDF5-WRF module
MuQun Yang, Robert E. McGrath, Mike Folk
National Center for Supercomputing Applications
University of Illinois, Urbana-Champaign

2. What is WRF?
• Weather Research and Forecasting Model –
Framework for Weather Model Community
• Primarily uses sequential I/O with NetCDF

3. Goal
• Provide an optional HDF5 IO module for
WRF
• Investigate IO performance of WRF

4. Results
• Map WRF data model to HDF5
• Implemented two WRF IO modules
– Sequential IO module with compression
– Parallel IO module
– Parallel IO module is include in WRF
distribution
• Performance studies
– Presented to WRF workshop, conferences

5. Findings
1. Parallel HDF5-WRF module can greatly reduce
wall clock time in some WRF applications.
2. Sequential HDF5-WRF module can greatly
reduce the WRF file size with szip or shuffling
and deflate compression algorithms.
3. Parallel HDF5 library needs to be improved for
chunking storage.

6. Impact
• Parallel HDF5 WRF I/O is available to
modelling community
– Included in WRF 2.0 source distribution (May
2004)
• This investigation has led to improvements
in Parallel HDF5

7. For more information
• HDF5 WRF IO:
http://hdf.ncsa.uiuc.edu/apps/WRF-ROMS
• WRF: http://www.wrf-model.org/

8. Acknowledgements
• This work is part of NSF-funded Modeling
Environment for Atmospheric Discovery
Expedition (MEAD)
(http://www.ncsa.uiuc.edu/AboutUs/Focus
Areas/MEADExpedition.html)