Nonblocking operations have successfully been used to hide network latencies in large scale parallel applications. This paper presents the challenges associated with developing nonblocking collective I/O operations, in order to help hiding the costs of I/O operations. We also present an implementation based on the libNBC library, and evaluate the benefits of nonblocking collective I/O over a PVFS2 file system for a micro-benchmark and a parallel image processing application. Our results

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... the potential benefit of our approach, but also highlight the challenges to achieve appropriate overlap between I/O and compute operations.