AtheOS File System

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The AtheOS file system (AFS) was originally used in the AtheOS operating system, and is now a part of the Syllable operating system. AFS started with exactly the same data structures as the Be File System, BFS, and extended its feature set in many ways. As such, AFS is a 64-bit journaled file system with support for file attributes. File indexing and soft deletions are also partially supported.

A few definitions:

  • Journaled -- All file system transactions are first written to a journal before they are executed. When mounted, the file system replays everything in the journal. So, if something catastrophic occurs as data is being written to the file system, the file system can recover.
  • File Attributes -- Name/value pairs tacked onto a file. For example, an audio file might have attributes for Artist, Title, and Album. This lets the file system search files in intelligent and flexible ways; example: search for all songs by Elton John that exist on the drive.
  • File Indexing -- A persistent and up-to-date list of all files with a specific attribute, and the value of that attribute. So, the system may have an index for the Artist attribute on MP3 files. This speeds searching, but slows system performance when large numbers of files are created.
  • Soft Deletions -- When the file system is told to delete a file, the file is actually hidden, and removed later by other means. In AFS, files are moved to an invisible directory and only deleted when the file system is next mounted.