If a large parallel job running on 640 PNs reads from/writes to one disk installed in a PN, each PN accesses to the disk in sequence and performance degrades terribly. Although local I/O in which each PN reads from or writes to its own disk solves theproblem, it is a very hard work to manage such a large number of partial files. ThenES adopts Staging and Global File System(GFS) that offers a high-speed I/O performance.