This talk presents the design and implementation of an asynchronous data-staging strategy for
file accesses based on ROMIO, the most popular MPI-IO distribution, and ZOID, the I/O forwarding component
of ZeptoOS, an open source operating system solution for Blue Gene systems. We describe and evaluate
a two-level file write-back and prefetching solution. The experimental results demonstrate that our
approach achieves high performance through a high degree of overlap between computation, communication,
and file I/O.