April 19, 2014
 
 
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Modern Distributed Filesystems For Linux: An Introduction - page 5

What Are Distributed Filesystems?

  • August 7, 2002
  • By Bill von Hagen

Before distributed filesystems, filesharing across a network was limited to simple file transfers using protocols such as the File Transfer Protocol (FTP). The World Wide Web has largely done away with the need for standalone file transfer commands by integrating the FTP protocol into most browsers. The ability to easily transfer files over the Web has also led to substantial research in using the Web and its underlying HyperText Transfer Protocol (HTTP) as the basis for distributed filesharing.

The best-known of these is WebDAV, which stands for Web-enabled Distributed Authoring and Versioning. WebDAV is a set of extensions to the HTTP protocol that provides a collaborative environment for users to access, manage, and edit files that are stored on Web servers.

WebDAV support is built into popular Web servers such as the Apache Web server, where it relies on the authentication mechanisms supported by the server, ranging from simple .htaccess files to integrated NIS, LDAP, or even Windows authentication. Using WebDAV to access and update files over the Web is built into operating systems such as Mac OS X, is supported in recent versions of Microsoft's Intenet Explorer, and is also available for Linux using applications such as the GNOME project's Nautilus file manager. While not a filesystem in the traditional sense, you can even mount WebDAV filesystems on Linux systems by using the davfs loadable kernel module.

WebDAV provides standard distributed computing features such as file locking, creating, renaming, copying, and deleting files, and also support advanced features such as file metadata, which is searchable information about the files on a WebDAV server, such as their title, subject, creator, and so on. In the near future, WebDAV will include integrated support for revision control, which will make it easier for multiple users to collaborate on shared files by tracking changes, their authors, and other aspects of shared document maintenance. These versioning capabilities are provided by the DeltaV protocol, which is actively under development by the DeltaV Working Group (http://www.webdav.org/deltav) of the Internet Engineering Task Force (IETF). Some projects, such as Subversion (http://subversion.tigris.org), a WebDAV and DeltaV-based replacement for the standard Unix/Linux Concurrent Versionsing System (CVS), are already available in Alpha form. Subversion provides versioning and a database-based file repository with a C-language API that simulates a versioned filesystem that is easily accessed over the Web.

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