DFSConcepts

DFSConcepts

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DFS stands for Distributed File System, a feature that lets you create a logical tree of shared-disk resources that are physically located on different computers on the network. DFS simplifies the task of managing shared-disk resources across a network and makes it easier for users to find and access these resources. From a user 's point of view, the DFS tree appears to be a single hierarchy of folders located on a single server while in actuality it may consist of shared folders on many different computers. Users don't need to know the computer on which a shared folder resides in order to access the folderthey simply connect to the DFS tree and access the folder. For example, documents for the sales department could be located on three different file servers on the network, but by implementing DFS, users can access these documents as if they were all stored on the same server.

DFS doesn't add any additional access control to the shared folders it manages . If users have suitable permissions to access a shared folder on the network, they can access it through DFS. However, when administrators add a DFS root or DFS link, they can specify who has permission to add new DFS links to the tree.

DFS Terminology

DFS trees consist of the following elements:

DFS namespace

Sometimes called a DFS tree, a hierarchical collection of shared resources consisting of a DFS root and one or more DFS links.

DFS target

The actual shared folder on the network to which a DFS root or link maps. The term "DFS target" replaces the term "DFS replica," which was used in W2K.

DFS root

The starting point for a DFS tree or namespace. Each DFS root maps to a DFS target, and clients can locate and access shared resources in DFS trees by browsing the root.

DFS link

A point beneath the root in a DFS tree or namespace. Each DFS link maps to one or more DFS targets.

In W2K Server, each machine could host only one DFS root. This is still the case for WS2003 Standard Edition, but machines running the Enterprise Edition can now host multiple DFS roots.

Types of DFS

There are two types of DFS you can use:

Standalone DFS

This method is used in small workgroup scenarios in which Active Directory has not been deployed. Configuration information for the DFS tree is stored on a single standalone server, and users locate and access shared resources by connecting to the DFS tree on the standalone server.

Domain-based DFS

Also called fault-tolerant DFS, this method is used in larger domain scenarios and stores DFS configuration information in Active Directory. Domain-based DFS automatically replicates this information to all domain controllers using standard Active Directory replication. Note that in domain-based DFS, client computers must be members of the domain where the DFS root is located.

DFS Replication

DFS replication uses the File Replication Service (FRS) to replicate content across multiple DFS trees. By creating additional targets for DFS roots, you can replicate the content of your DFS tree. This is done for two reasons:

• To provide fault tolerance in case a server hosting a DFS root goes down

• To provide load balancing so clients can access the nearest DFS tree

New to DFS in WS2003 is the ability to choose from four possible DFS replication topologies:

Ring

This is the default method and is ideal for single-site DFS.

Hub and Spoke

You might use this approach to replicate DFS from corporate headquarters to branch offices.

Full Mesh

Distributed enterprises might adopt this approach, but it can be difficult to troubleshoot.

Custom

You design what you want DFS to do.

DFS Clients

It's not enough to set up DFS on a server for it to work: the client computers that users use must also support DFS. DFS clients are available for the following Microsoft Windows operating systems:

WS2003, XP, and W2K

Includes DFS 5.0 client (fully functional)

NT 4.0 with Service Pack 3 or higher

Includes DFS 4.x/5.0 client (works with standalone DFS servers only)

Windows 98

Includes DFS 4.x/5.0 client (works with standalone DFS servers only), but a DFS 5.0 client that supports domain-based DFS servers as well can be downloaded from Microsoft's web site

Windows 95

Allows a downloadable DFS 4.x/5.0 client (works with standalone DFS servers only)

To use DFS, users connect to the root of the tree using any standard method of accessing shared folders and then browse it to find the child node they want to access. To connect to the DFS root, the client uses the DNS name of the host server for the root. From the user's point of view, DFS is like a series of folders located within one shared folder on one file server. In order to connect to a DFS tree, however, the client computer must be running DFS client software.

Clients access DFS roots on standalone DFS host servers by specifying the UNC path to the root. For example, if the DFS root named Files points to the shared folder Pub on member server George , then you would access the DFS root using \\George\Files . By contrast, for domain-based DFS, you specify the DNS name of the domain in the UNC path (e.g., \\mtit com\Files ).

Implementing DFS

To implement domain-based DFS, you might do this:

1. Create a DFS root on a domain controller or member server.

2. Add DFS links to shared folders on file servers in your domain.

3. Add a second DFS target to your root for fault tolerance and load balancing.

4. Configure replication between your DFS trees.