This paper presents a new approach towards parallel I/O for message-passing (MPI) applications on clusters built with commodity hardware and an SCI interconnect: instead of using the classic scheme of clients and a number of servers communicating via TCP/IP, a pure peer-to-peer communication topology based on efficient use of the underlying SCI interconnect is presented. Every process of the MPI application is client as well as server for I/O operations. This allows for a maximum of locality in file access, while the accesses to remote portions of the distributed file are performed via distributed shared memory techniques. A server is only required to manage the initial distribution of the file fragments between the participating nodes and to provide services like external access and redundancy. Keywords- cluster, SCI, parallel IO, MPI-IO, ROMIO, DSM