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Parallel file subsystems in today's high-performance computers adopt many I/O optimization strategies that were designed for distributed systems. These strategies, for instance client-side file caching, treat each I/O request process independently, due to the consideration that clients are unlikely related with each other in a distributed environment. However, it is inadequate to apply such strategies directly in the high-performance computers where most of the I/O requests come from the processes that work on the same parallel applications. We believe that client-side caching could perform more effectively if the caching subsystem is aware of the process scope of an application and regards all the application processes as a single client. In this paper, we propose the idea of "collective caching" which coordinates the application processes to manage cache data and achieve cache coherence without involving the I/O servers. To demonstrate this idea, we implemented a collective caching subsystem at user space as a library, which can be incorporated into any message passing interface implementation to increase its portability. The performance evaluation is presented with three I/O benchmarks on an IBM SP using its native parallel file system, GPFS. Our results show significant performance enhancement obtained by collective caching over the traditional approaches.