Parallel IO in Code_Saturne

Charles Moulinec, STFC Daresbury Laboratory

Code_Saturne is a multipurpose CFD software which has been ported on the fastest HPC machines. The solver has demonstrated very good speed-up for over 1.5 million processors of Argonne BG/Q, using a 13 billion cell mesh and on up to 72,000 cores of ARCHER, using a 0.9 billion cell mesh.

Ways around have been found to generate large meshes (on-the-fly mesh multiplication, for instance) and to postprocess data (co-processing). However, dumping the whole flow field for checkpoints on the disk seems unvoidable.

Two IO strategies exist in Code_Saturne, the former based on blocks of data collected from each process and the latter based on MPI-IO.

Comparison of IO performance observed on Lustre and GPFS systems will be presented, for different size of meshes.