Versioning File System

Conceptually, a versioning file system is similar to a periodic backup, with several key differences. First, backups normally go to separate media; versioning file systems write to the same hard drive (and normally the same folder, directory, or local partition). Second, backups are normally triggered on a timed basis; versioning occurs when the file changes. Third, backups are usually system-wide or partition-wide; versioning occurs independently on a file-by-file basis.

Versioning file systems provide some of the features of Revision Control System s. However, unlike most revision control systems, they are Transparent .

See Wayback for an example of a versioning file system.

Another different example is ext3cow that takes a snapshots of the entire file system.

A simple but powerful example of a file versioning system is built into the VMS operating system from Digital Equipment Corporation (DEC). In essence, whenever an application opens a file for writing, the file system automatically creates a new instance of the file, with a version number appended to the name. Version numbers start at 1 and count upward automatically as new instances of a file are created. When an application opens a file for reading, it can either specify the exact file name including version number, or just the file name without the version number, in which case the most recent instance of the file is opened. The file system automatically deletes sufficiently old versions of a file when a new instance is created; the maximum number of files retained is configurable, with an upper limit of 32,767.

Versioning filesystems should not be confused with Journaling File System s.

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Versioning File System