Beating the I/O bottleneck: a case for log-structured file systems

CPU speeds are improving at a dramatic rate, while disk speeds are not. This technology shift suggests that many engineering and office applications may become so I/O-limited that they cannot benefit from further CPU improvements. This paper discusses several techniques for improving I/O performance, including caches, battery-backed-up caches, and cache logging. We then examine in particular detail an approach called log-structured file systems , where the file system's only representation on disk is in the form of an append-only log. Log-structured file systems potentially provide order-of-magnitude improvements in write performance. When log-structured file systems are combined with arrays of small disks (which provide high bandwidth) and large main-memory file caches (which satisfy most read accesses), we believe it will be possible to achieve 1000-fold improvements in I/O performance over today's systems.