This paper presents the design and evaluation of aStriped File I/O (SFIO) library for parallel I/O within anMPI environment. We present techniques for optimizingcommunications and disk accesses for small striping factors.Using MPI derived datatype capabilities, we transmitfragmented data over the network by single MPI transfers.We present the I/O performance of the SFIO library onDEC Alpha clusters, both for the Fast Ethernet and for theTNET communication networks.