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Wikipedia

Coda (file system)

December 11, 2023

Coda is a distributed file system developed as a research project at Carnegie Mellon University since 1987 under the direction of Mahadev Satyanarayanan. It descended directly from an older version of Andrew File System (AFS-2) and offers many similar features. The InterMezzo file system was inspired by Coda.

Initial release1987; 36 years ago (1987)
Stable release
8.0.2[1] / May 29, 2020; 3 years ago (2020-05-29)
Repositorygithub.com/cmusatyalab/coda
Written inC
TypeDistributed file system
LicenseGPL v2
Websitecoda.cs.cmu.edu

Features edit

Coda has many features that are desirable for network file systems, and several features not found elsewhere.

  1. Disconnected operation for mobile computing.
  2. Is freely available under the GPL[2]
  3. High performance through client-side persistent caching
  4. Server replication
  5. Security model for authentication, encryption and access control
  6. Continued operation during partial network failures in server network
  7. Network bandwidth adaptation
  8. Good scalability
  9. Well defined semantics of sharing, even in the presence of network failure

Coda uses a local cache to provide access to server data when the network connection is lost. During normal operation, a user reads and writes to the file system normally, while the client fetches, or "hoards", all of the data the user has listed as important in the event of network disconnection. If the network connection is lost, the Coda client's local cache serves data from this cache and logs all updates. This operating state is called disconnected operation. Upon network reconnection, the client moves to reintegration state; it sends logged updates to the servers. Then it transitions back to normal connected-mode operation.

Also different from AFS is Coda's data replication method. AFS uses a pessimistic replication strategy with its files, only allowing one read/write server to receive updates and all other servers acting as read-only replicas. Coda allows all servers to receive updates, allowing for a greater availability of server data in the event of network partitions, a case which AFS cannot handle.

These unique features introduce the possibility of semantically diverging copies of the same files or directories, known as "conflicts". Disconnected operation's local updates can potentially clash with other connected users' updates on the same objects, preventing reintegration. Optimistic replication can potentially cause concurrent updates to different servers on the same object, preventing replication. The former case is called a "local/global" conflict, and the latter case a "server/server" conflict. Coda has extensive repair tools, both manual and automated, to handle and repair both types of conflicts.

Supported platforms edit

Coda has been developed on Linux and support for it appeared in the 2.1 Linux kernel series.[3] It has also been ported to FreeBSD. Subsequently, obsoleted there, an effort is under way to bring it back.[4] Efforts have been made to port Coda to Microsoft Windows, from the Windows 95/Windows 98 era, Windows NT[5] to Windows XP,[6] by means of open-source projects like the DJGCC DOS C Compiler and Cygwin.[5]

References edit

  1. ^ "Coda progress". July 5, 2020. Retrieved August 5, 2020.
  2. ^ "New release: 5.0.pre1". 1999-01-06. Retrieved 2015-09-11.
  3. ^ "Linux Kernel mailing list, [PATCH] Coda". 1998-01-06.
  4. ^ "GitHub - trasz/Freebsd at coda". GitHub.
  5. ^ a b Braam, P. J.; et al. (1999). "Porting the coda file system to windows". Proc. USENIX Annual Technical Conference. USENIX Association: 30. Retrieved 2009-04-15.
  6. ^ "Coda Support for Windows XP". Retrieved 2009-04-15.

External links edit

  • Coda website at Carnegie Mellon University
  • Coda: a highly available file system for a distributed workstation network, Mahadev Satyanarayanan James J. Kistler, Puneet Kumar, IEEE Transactions on Computers, Vol. 39, No. 4, April 1990
  • The Coda Distributed Filesystem for Linux 2005-03-08 at the Wayback Machine, Bill von Hagen, October 7, 2002.
  • The Coda Distributed File System with Picture representation, Peter J. Braam, School of Computer Science,

December 11, 2023
coda, file, system, this, article, needs, updated, please, help, update, this, article, reflect, recent, events, newly, available, information, september, 2013, coda, distributed, file, system, developed, research, project, carnegie, mellon, university, since,. This article needs to be updated Please help update this article to reflect recent events or newly available information September 2013 Coda is a distributed file system developed as a research project at Carnegie Mellon University since 1987 under the direction of Mahadev Satyanarayanan It descended directly from an older version of Andrew File System AFS 2 and offers many similar features The InterMezzo file system was inspired by Coda CodaDeveloper s Carnegie Mellon UniversityIntroduced1987OtherSupportedoperating systemsLinux kernel NetBSD FreeBSDInitial release1987 36 years ago 1987 Stable release8 0 2 1 May 29 2020 3 years ago 2020 05 29 Repositorygithub wbr com wbr cmusatyalab wbr codaWritten inCTypeDistributed file systemLicenseGPL v2Websitecoda wbr cs wbr cmu wbr edu Contents 1 Features 2 Supported platforms 3 References 4 External linksFeatures editCoda has many features that are desirable for network file systems and several features not found elsewhere Disconnected operation for mobile computing Is freely available under the GPL 2 High performance through client side persistent caching Server replication Security model for authentication encryption and access control Continued operation during partial network failures in server network Network bandwidth adaptation Good scalability Well defined semantics of sharing even in the presence of network failureCoda uses a local cache to provide access to server data when the network connection is lost During normal operation a user reads and writes to the file system normally while the client fetches or hoards all of the data the user has listed as important in the event of network disconnection If the network connection is lost the Coda client s local cache serves data from this cache and logs all updates This operating state is called disconnected operation Upon network reconnection the client moves to reintegration state it sends logged updates to the servers Then it transitions back to normal connected mode operation Also different from AFS is Coda s data replication method AFS uses a pessimistic replication strategy with its files only allowing one read write server to receive updates and all other servers acting as read only replicas Coda allows all servers to receive updates allowing for a greater availability of server data in the event of network partitions a case which AFS cannot handle These unique features introduce the possibility of semantically diverging copies of the same files or directories known as conflicts Disconnected operation s local updates can potentially clash with other connected users updates on the same objects preventing reintegration Optimistic replication can potentially cause concurrent updates to different servers on the same object preventing replication The former case is called a local global conflict and the latter case a server server conflict Coda has extensive repair tools both manual and automated to handle and repair both types of conflicts Supported platforms editCoda has been developed on Linux and support for it appeared in the 2 1 Linux kernel series 3 It has also been ported to FreeBSD Subsequently obsoleted there an effort is under way to bring it back 4 Efforts have been made to port Coda to Microsoft Windows from the Windows 95 Windows 98 era Windows NT 5 to Windows XP 6 by means of open source projects like the DJGCC DOS C Compiler and Cygwin 5 References edit Coda progress July 5 2020 Retrieved August 5 2020 New release 5 0 pre1 1999 01 06 Retrieved 2015 09 11 Linux Kernel mailing list PATCH Coda 1998 01 06 GitHub trasz Freebsd at coda GitHub a b Braam P J et al 1999 Porting the coda file system to windows Proc USENIX Annual Technical Conference USENIX Association 30 Retrieved 2009 04 15 Coda Support for Windows XP Retrieved 2009 04 15 External links editCoda website at Carnegie Mellon University Coda a highly available file system for a distributed workstation network Mahadev Satyanarayanan James J Kistler Puneet Kumar IEEE Transactions on Computers Vol 39 No 4 April 1990 The Coda Distributed Filesystem for Linux Archived 2005 03 08 at the Wayback Machine Bill von Hagen October 7 2002 The Coda Distributed File System with Picture representation Peter J Braam School of Computer Science Retrieved from https en wikipedia org w index php title Coda file system amp oldid 1182251950, wikipedia, wiki, book, books, library,

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