Log-structured file system: Difference between revisions

Revision as of 01:03, 13 June 2005

Revision as of 13:36, 12 July 2005

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A '''log-structured filesystem''' is a [[file system]] design first proposed by [[John K. Ousterhout]] and [[Fred Douglis]].

Conventional filesystems tend to lay out files on disk with great care for spatial locality and make in-place changes to data structures on disk in order to minimize read seeks on magnetic media. The design of a log-structured filesystems is based on the hypothesis that this would no longer be effective as ever-increasing memory sizes on modern computers would lead to disk I/O becoming write-heavy because disk reads would be almost always satisfied byfrom memory cache.

To maximize write throughput, a log-structured file system treats the disk as a circular log and writes sequentially to the head of the log. This has the side effect of creating multiple, chronologically-advancing versions of both file data and meta-data. Thus, a log-structured file system is a [[journaling filesystem]] in that the entire file system is a journal.

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* Tend to have good write performance.

[[John K. Ousterhout]] and [[Mendel Rosenbaum]] implemented the first log-structured file system for the [[Sprite operating system]] in 1992. AAn versionimplementation by [[Margo Seltzer]], the [[Log-structured File System]], was added later to 4.4BSD, and thence was ported to [[NetBSD]]. See [[Log-structured File System]] for a descripton of the [[NetBSD]] implementation.

== References ==