Parallel I∕O in Flexible Modelling System (FMS) and Modular Ocean Model 5 (MOM5)

Yang, Rui; Ward, Marshall; Evans, Ben

We present an implementation of parallel inline-formulaI∕O in the Modular Ocean Model (MOM), a numerical ocean model used for climate forecasting, and determine its optimal performance over a range of tuning parameters. Our implementation uses the parallel API of the netCDF library, and we investigate the potential bottlenecks associated with the model configuration, netCDF implementation, the underpinning MPI-IO library/implementations and Lustre filesystem. We investigate the performance of a global 0.25inline-formula resolution model using 240 and 960 CPUs. The best performance is observed when we limit the number of contiguous inline-formulaI∕O domains on each compute node and assign one MPI rank to aggregate and to write the data from each node, while ensuring that all nodes participate in writing this data to our Lustre filesystem. These best-performance configurations are then applied to a higher 0.1inline-formula resolution global model using 720 and 1440 CPUs, where we observe even greater performance improvements. In all cases, the tuned parallel inline-formulaI∕O implementation achieves much faster write speeds relative to serial single-file inline-formulaI∕O, with write speeds up to 60 times faster at higher resolutions. Under the constraints outlined above, we observe that the performance scales as the number of compute nodes and inline-formulaI∕O aggregators are increased, ensuring the continued scalability of inline-formulaI∕O-intensive MOM5 model runs that will be used in our next-generation higher-resolution simulations.



Yang, Rui / Ward, Marshall / Evans, Ben: Parallel I∕O in Flexible Modelling System (FMS) and Modular Ocean Model 5 (MOM5). 2020. Copernicus Publications.


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