"There's something both exciting and frightening about the announcement of a new Linux file system. It's exciting because file systems represent new territory for interesting advances. It's frightening because a file system in the early stages tends to be experimental and not quite ready for prime time. But sometimes these announcements are about investments in the future of Linux, and a recent announcement for 2.6.30-rc1 indicates a very interesting future, indeed. In the past few quarters, Linux has had three major file system announcements. Late 2008 brought in the B-Tree File System (Btrfs), and more recently, two other unique file systems were introduced: NiLFS(2) and exofs.
"File system background
"Let's start with a quick introduction to these non-traditional file system approaches, and then explore the specifics of NiLFS(2) and exofs.
"Log-structured file systems
"Log-structured file systems have a rich history in modern computing systems. The first log-structured file system was proposed by John Ousterhout and Fred Douglis in 1988 and subsequently implemented in the Sprite operating system in 1992. As the name implies, a log-structured file system views the file system as a circular log in which new data and file system metadata are written to the head of the log, and free space is reclaimed from the tail (see Figure 1). This means that data may appear two or more times in the log, but as the log is chronologically advancing, the most recent data is viewed as the active data. Having multiple copies of data in the log introduces some interesting benefits, which will be covered in more detail below."
