Characterizing the I/O Behavior of Scientific Applications on the Cray XT

Scientific applications use Input/Output (I/O) for obtaining initial conditions and execution parameters, as a persistent way of saving program output, and for safeguarding against system unreliability. Although system sizes are expected to continue increasing, I/O performance is not expected to keep pace with system computation and communication performance. Understanding application I/O demands and system I/O capabilities is the first step toward bridging this gap between them. In this paper, the authors present their approach for characterizing the I/O demands of applications on the Cray XT. They also present preliminary case studies showing the use of their I/O characterization infrastructure with climate studies and combustion simulation programs.