Informed Prefetch

increasingly depend on I/O-subsystem performance [Patterson88]. Unfortunately, simply growing the cache does not decrease cache-miss ratios as much as one might expect. For example, the Sprite group’s 1985 caching study led them to predict higher hit ratios for larger caches. But in 1991, after larger caches had been installed, hit ratios were not much changed — files had grown just as fast as the caches [Ousterhout85, Baker91]. This suggests that new tech-niques are needed to boost I/O performance. The problem is especially acute for read-intensive applica-tions. Write performance is less critical because the writing appli-cation generally does not wait for the disk to be written. In this common case, write behind can exploit storage parallelism eve