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DFS (Distributed File System)

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There are two file systems that take the acronym "DFS:" The Open Group's DFS and Microsoft's DFS. While they are both distributed file systems, they have little in common.

The Open Group DFS (Distributed File System)

DFS (Distributed File System) from The Open Group is a version of the AFS (Andrew File System) that is included with The Open Group's DCE (Distributed Computing Environment). Transarc is responsible for DFS. Its Web site is Refer to "AFS (Andrew File System)" for more information. Also refer to "Open Group" and "DCE (Distributed Computing Environment)."

Microsoft DFS (Distributed File System)

Microsoft DFS is designed to make it easier to access files on networks. It provides a way to unite files on different computers under a single name space. To the user, files appear as if they are in one location, rather than on separate computers. A hierarchical tree provides a view of these files, and users can "drill down" through the tree to find just the information they are looking for.

The user does not need to know or care about the physical location of the file, only where it is located in the hierarchical view. That means that users no longer search for files by opening file servers and disk drives, and looking through a separate directory structure on each. Instead, users look through a logical directory that places shared information in a place that makes more sense to users and administrators alike. With DFS, an administrator does up-front work to logically organize information, so users don't have trouble finding it later on.

As an analogy, think of a city library system in which the book catalog at each library lists all the books available at libraries throughout the city. You can order any book and it will be delivered from its current location. The important point is that there is one library catalog system that provides a list of all the books available, no matter what their physical location. DFS provides a single "catalog" view of files on your network, no matter where those files are located.

Some of the benefits of DFS are outlined here:

  • In Windows 2000, DFS takes advantage of the Active Directory. The DFS tree topology is automatically published to the Active Directory, resulting in fault tolerance for the DFS root.

  • Users can access information with DFS's hierarchical view of network resources. Administrators can create custom views to make file access easier for users.

  • Volumes consist of individual shares, and those shares can be at many different locations. A share can be taken offline without affecting the rest of the volume. The volumes that you add to a DFS root are the leaves or branch nodes that represent shared network directories.

  • User access to DFS volumes is controlled with standard Windows NT/Windows 2000 security, such as group access rights.

  • To ensure that critical data is always available, administrators can set up alternate locations for accessing data by simply including the alternate locations under the same logical DFS name. Client software automatically chooses to use data on a server that is closest to the user. If one of the locations goes down, another location is automatically selected.

  • Response time can be improved by load balancing the system. Often-accessed files can be stored in multiple locations, and the system will automatically distribute requests across the drives to balance traffic during peak usage periods.

  • Users don't need to know about the physical location of files. Administrators can physically move files to other drives; but to the user, the files still appear under the same location in the hierarchical tree.

  • Client access to shares is cached to improve performance. The first time a user accesses a published directory, the information is cached and used for future references.

  • DFS simplifies enterprise backups. Since a DFS tree can be built to cover an entire enterprise, the backup software can back up this single "tree," no matter how many servers/shares are part of the tree. The tree can include Windows 95 and Windows NT/Windows 2000 desktops as well.

  • A graphical administration tool makes it easy to configure volumes, DFS links, and remote DFS roots.

DFS fits into an organization's Internet and intranet strategy. The Web page of individual departments or even users can be included within the directory tree. DFS can also hold HTML links; so, if linked pages are moved to a different physical location, all links pointing to the pages will not have to be reconfigured.

DFS Volumes

A DFS volume starts out by being hosted by a specific computer. There may be many individual DFS volumes available on a network, and each will have its own distinct name. Windows NT/Windows 2000 servers are currently the only systems that can host DFS volumes. An organization might have a master DFS volume that contains links to other DFS volumes at the department or division level. Another volume might tie together shares that are common in each department, such as public documents.

In the DFS volume name shown here, the hosting computer name is Server_Name:

\\Server_Name\DFS Share Name\path\name

Like a local file system, a DFS volume has a root that is its starting point. This is represented by DFS_Share_Name. The reference to path\name can be any valid pathname.

Figure D-20 illustrates how links work. Three departments-Marketing, Engineering, and Research-have set up their own name spaces to fit their own needs. The corporate DFS volume links into specific parts of these shares as needed to provide corporate users with information from other locations in the organization. When a link is accessed, the junction between two different DFS volumes is crossed and the server that provides the DFS root changes. This is transparent to the user, however.

Figure 20: See book

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.