An Implementation and Evaluation of Client-Side File Caching for MPI-IO

Client-side file caching has long been recognized as a file system enhancement to reduce the amount of data transfer between application processes and I/O servers. However, caching also introduces cache coherence problems when a file is simultaneously accessed by multiple processes. Existing coherence controls tend to treat the client processes independently and ignore the aggregate I/O access pattern. This causes a serious performance degradation for parallel I/O applications. In this paper we discuss our new implementation and present an extended performance evaluation on GPFS and Lustre parallel file systems. In addition to comparing our methods to traditional approaches, we examine the performance of MPI-IO caching under direct I/O mode to bypass the underlying file system cache. We also investigate the performance impact of two file domain partitioning methods to MPI collective I/O operations: one which creates a balanced workload and the other which aligns accesses to the file system stripe size. In our experiments, alignment results in better performance by reducing file lock contention. When the cache page size is set to a multiple of the stripe size, MPI-IO caching inherits the same advantage and produces significantly improved I/O bandwidth.