Improvements in the processing speed of multiprocessors are outpacing improvements in the speed of disk hardware. Parallel disk I/O subsystems have been proposed as one way to close the gap between processor and disk speeds. In a previous paper we showed that prefetching and caching have the potential to deliver the performance bene ts of parallel le systems to parallel applications. In this paper we describe experiments with practical prefetching policies, and show that prefetching can be implemented e ciently even for the more complex parallel le access patterns. We also test the ability of these policies across a range of architectural parameters.