It has been suggested that OpenAFS be merged into this article or section. (Discuss)

The Andrew File System (AFS) is a distributed networked file system developed by Carnegie Mellon University as part of the Andrew Project. It is named for Andrew Carnegie and Andrew Mellon. Its primary use is in distributed computing. Image File history File links Please see the file description page for further information. ... OpenAFS is an open source implementation of the Andrew file system (AFS). ... // For the Microsoft distributed file system (DFS), see Distributed File System (Microsoft). ... Carnegie Mellon University is a private research university located in Pittsburgh, Pennsylvania. ... // The Information Technology Center was a joint project of Carnegie Mellon University and IBM to develop and deploy a distributed computing environment on the Carnegie Mellon campus. ... Andrew Carnegie (November 25, 1835 – August 11, 1919) was a Scottish industrialist, businessman, a major philanthropist, and the founder of Pittsburghs Carnegie Steel Company which later became U.S. Steel. ... Andrew William Mellon (March 24, 1855 — August 27, 1937) was an American banker, industrialist, philanthropist, art collector and Secretary of the Treasury from March 4, 1921 until February 12, 1932. ... Distributed computing is a method of computer processing in which different parts of a program run simultaneously on two or more computers that are communicating with each other over a network. ...

Features

AFS has several benefits over traditional networked file systems, particularly in the areas of security and scalability. It is not uncommon for enterprise AFS cells to exceed fifty thousand clients^{[citation needed]}. AFS uses Kerberos for authentication, and implements access control lists on directories for users and groups. Each client caches files on the local filesystem for increased speed on subsequent requests for the same file. This also allows limited filesystem access in the event of a server crash or a network outage. ^[1] It has been suggested that Crash counting be merged into this article or section. ... Kerberos is a computer network authentication protocol, which allows individuals communicating over an insecure network to prove their identity to one another in a secure manner. ... In computer security, an access control list (ACL) is a list of permissions attached to an object. ...

Read and write operations on an open file are directed only to the locally cached copy. When a modified file is closed, the changed portions are copied back to the file server. Cache consistency is maintained by a mechanism called callback. When a file is cached the server makes a note of this and promises to inform the client if the file is updated by someone else. Callbacks are discarded and must be re-established after any client, server, or network failure, including a time-out. Re-establishing a callback involves a status check and does not require re-reading the file itself.

A consequence of the whole file locking strategy is that AFS does not support large shared databases or record updating within files shared between client systems. This was a deliberate design decision based on the perceived needs of the university computing environment. It leads, for example, to the use of a single file per message in the original email system for the Andrew Project, the Andrew Message System, rather than the more customary single file per mailbox. File locking is a mechanism that enforces access to a computer file by only one user or process at any specific time. ...

A significant feature of AFS is the volume, a tree of files, sub-directories and AFS mountpoints (links to other AFS volumes). Volumes are created by administrators and linked at a specific named path in an AFS cell. Once created, users of the filesystem may create directories and files as usual without concern for the physical location of the volume. A volume may have a quota assigned to it in order to limit the amount of space consumed. As needed, AFS administrators can move that volume to another server and disk location without the need to notify users; indeed the operation can occur while files in that volume are being used. Introduction and Definition In the context of computer operating systems, volume is the term used to describe a single accessible storage area with a single filesystem, typically (though not necessarily) resident on a single partition of a hard disk. ... Mounting, in computer science, is the process of making a file system ready for use by the operating system, typically by reading certain index data structures from storage into memory ahead of time. ... A disk quota is a limit set by a system administrator that restricts certain aspects of file system usage on modern operating systems. ...

AFS volumes can be replicated to read-only cloned copies. When accessing files in a read-only volume, a client system will retrieve data from a particular read-only copy. If at some point that copy becomes unavailable, clients will look for any of the remaining copies. Again, users of that data are unaware of the location of the read-only copy; administrators can create and relocate such copies as needed. The AFS command suite guarantees that all read-only volumes contain exact copies of the original read-write volume at the time the read-only copy was created.

The file name space on an Andrew workstation is partitioned into a shared and local name space. The shared name space (usually mounted as /afs on the Unix filesystem) is identical on all workstations. The local name space is unique to each workstation. It only contains temporary files needed for workstation initialization and symbolic links to files in the shared name space.

The Andrew File System heavily influenced Version 4 of Sun Microsystems' popular Network File System (NFS). Additionally, a variant of AFS, the Distributed File System (DFS) was adopted by the Open Software Foundation in 1989 as part of their Distributed computing environment. Sun Microsystems, Inc. ... Network File System (NFS) is a network file system protocol originally developed by Sun Microsystems in 1984, allowing a user on a client computer to access files over a network as easily as if the network devices were attached to its local disks. ... The DCE Distributed File System (DCE/DFS) is the remote file access protocol used with the Distributed Computing Environment. ... The Open Software Foundation (OSF) was an organization founded in 1988 to create an open standard for an implementation of the Unix operating system. ... The Distributed Computing Environment (DCE) is a software system developed in the early 1990s by a consortium that included Apollo Computer (later part of Hewlett-Packard), IBM, Digital Equipment Corporation, and others. ...

Implementations

There are three major implementations, Transarc (IBM), OpenAFS and Arla, although the Transarc software is losing support and is deprecated. AFS (version two) is also the predecessor of the Coda file system. An editor has expressed a concern that the subject of the article does not satisfy the notability guideline or one of the following guidelines for inclusion on Wikipedia: Biographies, Books, Companies, Fiction, Music, Neologisms, Numbers, Web content, or several proposals for new guidelines. ... International Business Machines Corporation (IBM, or colloquially, Big Blue) (NYSE: IBM) (incorporated June 15, 1911, in operation since 1888) is headquartered in Armonk, New York, USA. The company manufactures and sells computer hardware, software, and services. ... OpenAFS is an open source implementation of the Andrew file system (AFS). ... Arla is an implementation of the AFS file system developed at the Royal Institute of Technology in Stockholm. ... Coda is a distributed filesystem, developed at Carnegie Mellon University since 1987, under the direction of Mahadev Satyanarayanan. ...

A fourth implementation exists in the Linux kernel source code since at least version 2.6.10^[2]. Committed by Red Hat, this is a fairly simple implementation still in its early stages of development and therefore incomplete.^[3] Linux (IPA pronunciation: ) is a Unix-like computer operating system. ... A kernel connects the application software to the hardware of a computer. ... Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. ... Red Hat, Inc. ...

Available permissions

The following Access Control List permissions can be granted:

Lookup (l)

allows a user to list the contents of the AFS directory, examine the ACL associated with the directory and access subdirectories.

Insert (i)

allows a user to add new files or subdirectories to the directory.

Delete (d)

allows a user to remove files and subdirectories from the directory.

Administer (a)

allows a user to change the ACL for the directory. Users always have this right on their home directory, even if they accidentally remove themselves from the ACL.

Permissions that affect files and subdirectories include:

Read (r)

allows a user to look at the contents of files in a directory and list files in subdirectories. Files that are to be granted read access to any user, including the owner, need to have the standard UNIX "owner read" permission set.

Write (w)

allows a user to modify files in a directory. Files that are to be granted write access to any user, including the owner, need to have the standard UNIX "owner write" permission set.

Lock (k)

allows the processor to run programs that need to "flock" files in the directory. See the UNIX man page for "flock" for more details.

Additionally, AFS includes Application ACLs (A)-(H) which have no effect on access to files.

References

1. ^ Andrew File System definition at SearchStorage.com
2. ^ Linux kernel AFS documentation for 2.6.10
3. ^ Linux kernel AFS documentation for 2.6.20.1