Microsoft Distributed File System (Dfs) for Windows NT Server is a network server component that makes it easier for you to find and manage data on your network. Dfs is a means for uniting files on different machines into a single name space. Dfs makes it easy to build a single, hierarchical view of multiple file servers and file server shares on your network. Instead of seeing a physical network of dozens of file servers, each with a separate directory structure, users will now see a few logical directories that include all of the important file servers and file server shares. Each share appears in the most logical place in the directory, no matter what server it is actually on.
Dfs does for servers and shares what file systems do for hard disks. File systems provide uniform named access to collections of sectors on disks; Dfs provides a uniform naming convention and mapping for collections of servers, shares, and files. Thus, Dfs adds the capability of organizing file servers and their shares into a logical hierarchy, making it considerably easier for a large corporation to manage and utilize its information resources. In addition, Dfs is not limited to a single file protocol and can support the mapping of servers, shares, and files regardless of the file client being used, provided the client supports the native server and share to begin with.
What is a Distributed File System?
Dfs provides name transparency to disparate server volumes and shares. Through Dfs, an administrator can build a single hierarchical file system whose contents are distributed throughout your organization's WAN. In short, Dfs can be thought of as a share of other shares.
Historically, with UNC naming (universal naming convention), a user or application would specify the physical server and share in order to access file information; e.g., \\server\share\path\filename). Even though UNCs may be used directly, a UNC is typically mapped to a drive letter where "X:" might be mapped to \\server\share, and after, a user navigates beyond the redirected drive mapping to the data he or she wishes to access; e.g., copy X:\path\more path\…..\filename.
As networks continue to grow in size and as organizations begin to use existing storage, both internally and externally, for purposes such as intranets, the idea of mapping a single drive letter to individual shares scales poorly. And despite the ability for users to directly reference UNC naming, the true nature of the problem is that end users can become overwhelmed by the increasing number of places that must be accessed in order to retrieve data.
Dfs solves these problems by permitting the linking of servers and shares into a simpler, more meaningful namespace. This new Dfs volume permits shares to be hierarchically connected to other Windows NT shares. Since Dfs maps the physical storage into a logical representation, the net benefit is that the physical location of data becomes transparent to users and applications.
Benefits of Dfs
The features of Dfs and their benefits are outlined in detail in the following table.
Description | Benefits | ||
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By linking shares together, administrators can create a single hierarchical volume which behaves as though it were one giant hard drive. Individual users can create their own Dfs volumes, which in turn can be incorporated by other Dfs volumes. This is called Inter-Dfs links. |
Provides a simplified view of network shares that can be customized by the administrator. |
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Individual shares participating in the Dfs volume can be taken off-line without affecting the remaining portion of the volume namespace. |
Allows administrators to manage physical network shares, independent of their logical representation to users. |
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Each Dfs root is administered with an easy-to-use graphical administration tool which permits browsing, configuration of volumes, alternates, and inter-Dfs links, as well as administration of remote Dfs roots. |
Requires little training, reducing the need for trained, full-time server administrators. |
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Multiple copies of read-only shares can be mounted under the same logical Dfs name to provide alternate locations for accessing data. In the event that one of the copies becomes unavailable, an alternate will automatically be selected. |
Important business data is always available, even if a server, disk drive, or file occasionally fails. |
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Multiple copies of read-only shares on separate disk drives or servers can be mounted under the same logical Dfs name, thereby permitting limited load balancing between drives or servers. As users request files from the Dfs volume, they are transparently referred to one of the network shares comprising the Dfs volume. |
Automatically distributes file access across multiple disk drives or servers to balance loads and improve response time during peak usage periods. |
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End users navigate the logical namespace without consideration to the physical locations of their data. Physical data can be relocated to any server and the logical Dfs namespace can be re-configured so that the end user's perspective of the Dfs namespace is unaffected (that is, it is transparent to users that their data has changed location). |
Increased administrative flexibility. Administrators can move network shares between servers or disk drives without affecting users' ability to access the data. |
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No additional administrative or security issues. Any user which connects to a Dfs volume is only permitted to access files for which they have appropriate rights on that share. |
Uses the existing Windows NT Security model for easy administration and secure access. |
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The Dfs Windows NT Workstation client has been incorporated into Windows NT Workstation 4.0. This integration with the SMB redirector allows the extra Dfs functionality to be fully pageable, and does not affect memory needs or standard client access performance. |
Dfs functionality requires no additional resources on client systems. |
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A Dfs volume can potentially connect hundreds or thousands of published shares. The client software makes no assumptions over what portion of Dfs published information a user might access. As a result, the first access of a published directory caches certain information locally. The next time a client accesses that portion of the Dfs namespace, the cached referral is accessed rather than obtaining a new referral. |
High-performance access to complex hierarchies of network volumes. |
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In addition to the Dfs aware Windows NT Workstation redirector that ships with Windows NT Workstation 4.0, Dfs includes a Windows® 95 service to permit Windows 95 users to navigate the Dfs namespace. With the current release of Dfs, Windows 95 clients can only access non-SMB volumes via a server based gateway (e.g., Microsoft Gateway Services for NetWare which is included with Windows NT Server). |
Extends Dfs benefits to Windows 95 users. |
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Any volume that is accessible through a redirector on Windows NT Workstation can participate in the Dfs namespace. This can either be through client redirectors or server-based gateway technology. |
Administrators can create a single hierarchy incorporating heterogeneous network file systems. |