Implementation and evaluation of prefetching in the Intel Paragon parallel file system

The significant difference between the speeds of the I/O system (e.g. disks) and compute processors in parallel systems creates a bottleneck that lowers the performance of an application that does a considerable amount of disk accesses. A major portion of the compute processors´ time is wasted on waiting for I/O to complete. This problem can be addressed to a certain extent, if the necessary data can be fetched from the disk before the I/O call to the disk is issued. Fetching data ahead of time, known as prefetching in a multiprocessor environment depends a great deal on the application´s access pattern. The subject of this paper is implementation and performance evaluation of a prefetching prototype in a production parallel file system on the Intel Paragon. Specifically, this paper presents: the design and implementation of a prefetching strategy in the parallel file system; and performance measurements and evaluation of the file system with and without prefetching. The prototype is designed at the operating system level for the PFS. It is implemented in the PFS subsystem of the Intel Paragon Operating System. It is observed that in many cases prefetching provides considerable performance improvements. In some other cases no improvements or some performance degradation is observed due to the overheads incurred in prefetching