We would like to thank Doug Clark, Ed Grochowski, Ed Lee, Spencer Ng, Chandu Thekkath, Honesty Young, and the class participants of Princeton CS598e (spring 2000) for the early discussions on this topic, HP Labs for supplying the I/O traces, the OSDI reviewers for their comments, and John Wilkes for a large number of excellent suggestions during a meticulous and tireless shepherding process.