I/o characterization of a portable astrophysics application on the ibm sp and intel paragon

Many large-scale applications on parallel machines are bottlenecked by the I/O performance rather than the CPU or communication performance of the system. To improve the I/O perfor-mance, it is rst necessary for system designers to understand the I/O requirements of various applications. This paper presents the results of a study of the I/O characteristics and perfor-mance of a real, I/O-intensive, portable, parallel application in astrophysics, on two dierent parallel machines|the IBM SP and the Intel Paragon. We instrumented the source code to record all I/O activity, and analyzed the resulting trace les. Our results show that, for this application, the I/O consists of fairly large writes, and writing data to les is faster on the Paragon, whereas opening and closing les are faster on the SP. We also discuss how the I/O performance of this application could be improved; particularly, we believe that this application would benet from using collective I/O