Distributed File System

Microsoft Distributed file system (Dfs) is Windows 2000 Server software that makes it easier for you to find and manage data on your enterprise network. Dfs provides mapping and a uniform naming convention for collections of servers, shares, and files. Dfs adds the capability of organizing file servers and their shares into a logical hierarchy, making it considerably easier to manage and use information resources.

With Dfs, you can create a single directory tree that includes multiple file servers and file shares in a group, division, or enterprise. Any Windows 2000 server can host a Dfs root or Dfs volumes. A Dfs root is a local share that serves as the starting point and host to other shares. A network can host many individual Dfs volumes, each having a distinct name. A Dfs topology is a single Domain Name System (DNS) namespace. You can use a single topology or multiple Dfs topologies to distribute your organization's shared resources.

Dfs functionality is integrated with Active Directory; the Dfs topology is published to Active Directory. Because changes to a domain-based Dfs topology are automatically synchronized with Active Directory, you can always restore a Dfs topology if the Dfs root is offline for any reason. Computer-based Dfs stores the topology in the registry.

Dfs has the following features:

• Provides a simplified view of network shares that can be customized by the administrator.
• Allows Microsoft® Windows® 95 and Windows 98 clients to access shares by using server message block (SMB) protocol.
• Supports mounting replicas of network shares for load balancing and better data availability.

  Active Directory further optimizes network use by redirecting Active Directory–enabled clients to a Dfs share point within the client site.

• Integrates with the File Replication service (FRS) to permit optional replication of read/write data between multiple shares.
• Allows users to log on just once for multiple access.

You can access a Dfs volume by using a uniform naming convention (UNC) name. Although UNC names can be used, in most cases users will find it easier if they substitute a drive letter. For example, note the physical locations in relation to the logical paths shown in Table 19.3.

Table 19.3 Accessing a Dfs Volume

Since Dfs maps the physical storage into a logical representation, the physical location of data becomes transparent to users and applications. Dfs eliminates the need for users to know where information is physically stored. Because users do not need to know the name of a server or share, you can physically move user information to another server without reeducating users about how to find their data, thereby improving file management.

Considerations for Using Dfs in Your Storage Strategy

Consider the following advantages of using Dfs shares as part of your storage planning:

• Active Directory replicates the Dfs topologies for all domain-based Dfs topologies to each Dfs root server. This distributes the load on participating servers and implements fault tolerance for the Dfs root.
• Multiple servers can host domain-based Dfs roots and alternates. If a root fails, Dfs detects the failure and another server acquires the root. This failover process increases data availability.
• Multiple copies of shares on separate servers can be mounted under the same logical Dfs name. This provides alternate locations for accessing data, thereby providing for load balancing and better data availability.
• Multiple copies of shares also allow administrators to perform preventative maintenance on servers. A server hosting one replica can be taken offline without impacting users since Dfs automatically routes requests to a replica that is online.
• Dfs ensures that users go to the closest replica by distributing copies of your files by site. This reduces the load on the wide area network (WAN).
• Location transparency eases the burden of upgrading to new servers by allowing additional storage to be published in subdirectories.

Consider implementing Dfs if any of the following conditions exist in your organization:

• Users that access shared resources are distributed across a site or sites.
• Most users require access to multiple shared resources.
• Users require uninterrupted access to shared resources.
• Load balancing for your network could be improved by redistributing shared resources.
• Your organization has data that is stored on multiple network shares.

For more information about designing a Dfs tree, see Windows 2000 Server Help.

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