Since the definition of the MPI-IO, a standard interface for parallel IO, some implementations are available for cluster of workstations. In this paper we focus on the ROMIO implementation (from Argonne Laboratory), running on PVFS. PVFS [5] is a Parallel Virtual File System developed at Clemson University. This file system uses local file systems of I/O nodes in a cluster to store data on disks. Data is striped among disks with a stripe parameter. The ROMIO implementation is not aware of the particular data-distribution of PVFS. We show how to improve performances of collective I/O of MPI-IO on such a parallel and distributed file system: the optimization avoids the data-redistribution induced by the PVFS file system. We show performance results on typical file access schemes found in data-parallel applications, and compare to the performances of the original PVFS port.