Towards a High Performance Implementation of MPI-IO on the Lustre File System

Lustre is becoming an increasingly important file system for large-scale computing clusters. The problem is that many data-intensive applications use MPI-IO for their I/O requirements, and it has been well documented that MPI-IO performs poorly in a Lustre file system environment. However, the reasons for such poor performance are not currently well understood. We believe that the primary reason for poor performance is that the assumptions underpinning most of the parallel I/O optimizations implemented in MPI-IO do not hold in a Lustre environment. Perhaps the most important assumption that appears to be incorrect is that optimal performance is obtained by performing large, contiguous I/O operations. Our research suggests that this is often the worst approach to take in a Lustre file system. In fact, we found that the best performance is sometimes achieved when each process performs a series of smaller, non-contiguous I/O requests. In this paper, we provide experimental results showing that such assumptions do not apply in Lustre, and explore new approaches that appear to provide significantly better performance.