Y-lib

Abstract

It is widely known that MPI-IO performs poorly in a Lustre file system environment, although the reasons for such performance are currently not well understood. The research presented in this paper strongly supports our hypothesis that MPI-IO performs poorly in this environment because of the fundamental assumptions upon which most parallel I/O optimizations are based. In particular, it is almost universally believed that parallel I/O performance is optimized when aggregator processes perform large, contiguous I/O operations in parallel. Our research shows that this approach generally provides the worst performance in a Lustre environment, and that the best performance is often obtained when the aggregator processes perform a large number of small, non-contiguous I/O operations.