Implementation and Evaluation of File Write-Back and Prefetching for MPI-IO Over GPFS

In this paper we present the implementation of an open source MPI-IO interface for General Parallel File System (GPFS). Our solution includes the design and implementation of GPFS-based write-back and prefetching modules, which have been integrated in ROMIO. A collective file write strategy based on GPFS data-shipping, and a view-based collective I/O mechanism, relying on GPFS mechanisms, are at the core of the novel optimizations proposed in this paper. View-based collective I/O includes a thread-based flushing method implementing a write-back policy for latency hiding, and a prefetching method, based on GPFS hints, to increase small read access performance. Performance evaluations show that our implementation achieves high-performance and hides the latency of file accesses through the combination of view-based collective file accesses, and the overlapping of computation, communication and I/O. This is especially true for collective and small size access patterns, which are very frequent in parallel scientific applications.