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What Is DFS?

Updated: March 28, 2003

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

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One of the goals of most information technology (IT) groups is to manage file server resources efficiently while keeping them available and secure for users. As networks expand to include more users and servers—whether they are located in one site or in geographically distributed sites—administrators find it increasingly difficult to keep users connected to the files they need. On one hand, distributing resources across a network makes them more available to more people and promotes cross-organizational efforts. On the other hand, storing files on different file servers located throughout an organization makes it difficult for users to know where to look for information. Administrators also find it difficult to keep track of all the servers and all of the people who use those servers. The task of swapping out an old server becomes a major communication chore when users across an organization must be notified to update links and file paths.

To help administrators address these problems, Windows Server 2003 includes Distributed File System (DFS). DFS allows administrators to group shared folders located on different servers by transparently connecting them to one or more DFS namespaces. A DFS namespace is a virtual view of shared folders in an organization. Using the DFS tools, an administrator selects which shared folders to present in the namespace, designs the hierarchy in which those folders appear, and determines the names that the shared folders show in the namespace. When a user views the namespace, the folders appear to reside on a single, high-capacity hard disk. Users can navigate the namespace without needing to know the server names or shared folders hosting the data. DFS also provides other benefits, including the following:

Simplified data migration

DFS simplifies the process of moving data from one file server to another. Because users do not need to know the name of each physical server or shared folder that contains the data, administrators can physically move data to another server without needing to reconfigure applications and shortcuts and without needing to reeducate users about where they can find their data. This minimizes the impact of server consolidation on users. It also allows administrators to deploy additional file servers and present the folders on those new servers as new folders within an existing namespace.

Increased availability of file server data

In the event of a server failure, DFS refers client computers to the next available server, so users can always access shared folders without interruption.

Load sharing

DFS provides a degree of load sharing by mapping a given logical name to shared folders on multiple file servers. For example, suppose that \\Company\StockInfo is a heavily used shared folder. Administrators can use DFS to associate this location with multiple shared folders on different servers, even if the servers are located in different sites.

Security integration

Administrators do not need to configure additional security for DFS namespaces because file and folder security is enforced by existing the NTFS file system and shared folder permissions on each target. For example, a user navigating a DFS namespace is permitted to access only the files or folders for which he or she has appropriate NTFS or shared folder permissions.

Common DFS Scenarios

DFS is commonly used in the following scenarios:

Server Consolidation

Many organizations today are consolidating older file servers throughout the organization into fewer, larger, more powerful file servers. Consolidation reduces the cost of managing multiple file servers and increases the efficiency of storage allocation and backup tasks. Organizations that have implemented DFS can perform server consolidations without impacting the way users’ access data. The following figure illustrates this benefit.

How DFS Eliminates the Impact of Server Consolidation on Users

How DFS Eliminates Impact of Server Consolidation

Publishing Applications

DFS is commonly used to publish applications to users throughout the organization. Using DFS in this scenario provides a number of benefits, such as the ability to use multiple servers to host application data and distribute the load across servers. A feature in DFS known as “least expensive target selection” ensures that users are connected to the closest server. The following figure illustrates a DFS namespace used to publish applications in an organization based in San Francisco with offices in Miami and Dallas.

Using DFS to Publish Applications

Using DFS to Publish Applications

This organization has three types of software:

  • Business-critical software and operating systems that must be available at all times.

  • Previous versions of software that are still in use in the Dallas branch office.

  • Multimedia software used primarily in San Francisco.

The organization uses four servers to host the business-critical software and operating systems, including two servers in the San Francisco site. Using two servers to host the applications ensures that a failure on one server does not cause the data to become unavailable. All users can access this software at \\Software\Public\Applications, and users are automatically directed to the server in their site (San Francisco, Dallas, or Miami).

Because the archived software is used only in the Dallas office and the data is not business-critical, only a single server hosts that data. The multimedia software is not business-critical, but the organization uses two servers for this software to improve server response times because the client portion of the multimedia software accesses files from the server.

Increasing Data Availability

As described in the scenario for publishing applications, administrators can use DFS to increase the availability of data by storing the data on multiple servers. DFS makes this process transparent by presenting to users what appears to be a single folder in the namespace. Administrators can use File Replication service (FRS) or some other replication method, such as the Windows Resource Kit Tool Robocopy, to keep the data synchronized on the servers. If one of the servers hosting data is unavailable, clients are referred to another server that hosts the data.

Technologies Related to DFS

File Replication service (FRS) can be used to keep data in DFS shared folders synchronized among servers. However, DFS and FRS are two separate technologies, and DFS does not require FRS. You can use other replication methods, such as manual copying, the Resource Kit Tool Robocopy, or other replication tools to keep DFS shared folders synchronized. Conversely, if you want to use FRS to keep data in shared folders synchronized, you must use DFS.

DFS Dependencies

DFS has the following dependencies:

  • Active Directory replication. Domain-based DFS requires that Active Directory replication is working properly so that the DFS object resides on all domain controllers in the domain.

  • Server Message Block (SMB). Clients must access DFS root servers by using the SMB protocol.

  • Remote Procedure Call (RPC) service and Remote Procedure Call Locater service. The DFS tools use RPC to communicate with the DFS service running on DFS root servers.

  • Distributed File System service dependencies. The Distributed File System service must be running on all DFS root servers and domain controllers so that DFS can work properly. This service depends on the following services:

    • The Server service, Workstation service, and Security Accounts Manager (SAM) service on DFS root servers. The Distributed File System service also requires an NTFS volume to store the physical components of DFS on root servers.

    • The Server service and Workstation service on domain controllers.

Related Information

The following resources contain additional information that is relevant to this section.

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