Distributed File System: Namespace Availability Questions
Published: August 3, 2011
Updated: August 3, 2011
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2008, Windows Server 2008 R2
This FAQ answers questions about namespace availability in Distributed File System (DFS) namespaces. For other questions, see DFS Namespaces: Frequently Asked Questions.
The answer depends on type of namespace: stand-alone or domain-based.
For stand-alone DFS namespaces, you ensure the availability of a stand-alone DFS root by creating it on the cluster storage of a clustered file server by using the Cluster Administrator snap-in.
For domain-based DFS namespaces, you ensure the availability of domain-based DFS roots by creating multiple root targets on non-clustered file servers or on the local storage of the nodes of server clusters. (Domain-based DFS roots cannot be created on cluster storage.) All root targets must belong to the same domain. To create root targets, use the Distributed File System snap-in or the Dfsutil.exe command-line tool.
To ensure the availability of domain-based DFS roots, you must have at least two domain controllers and two root targets within the domain that is hosting the root. If you have only one domain controller and it becomes unavailable, the namespace is inaccessible. Similarly, if you have only a single root target, and the server hosting the root target is unavailable, the namespace is also unavailable.
There are two ways to increase the availability of data in link targets:
Create a single link that points to a link target on a clustered file server.
Create multiple link targets and replicate content among them.
You can create link targets that point to clustered file servers in both types of namespaces. However, if you want to replicate content among multiple link targets, the type of namespace determines your replication options.
In a stand-alone DFS namespace, you can replicate the files by copying them manually, using scripts, using Robocopy.exe, which is available in the Microsoft Windows Server 2003 Deployment Kit, or by using other replication tools. The Distributed File System snap-in does not provide a user interface for configuring FRS replication in stand-alone DFS namespaces. To configure replication manually, consult the documentation supplied with your replication tools.
The Distributed File System snap-in in Windows Server 2003 provides a user interface for creating the FRS topology and schedule on servers running Windows Server 2003. Using FRS in a domain-based DFS namespace is optional; you can also replicate files by copying them manually or by using non-Microsoft replication tools.
If a DFS client attempts to access a previously used target, and that target is unavailable, the DFS client works down through its referral list for the next available target. This process is often referred to as link target or root target failover. If the client reaches the end of the referral list (that is, there are no available targets), the DFS client fails the request.
Because stand-alone DFS namespaces can have only one root target, no failover occurs if the stand-alone root server is not available; in that case, clients cannot access the namespace.
For link target failover to work correctly, each link can have targets that correspond to only one of the following locations:
One or more shared folders.
One or more stand-alone DFS paths anywhere in the stand-alone DFS namespace, including the root.
A single domain-based DFS path anywhere in the domain-based DFS namespace, including the root.
For root target failover to work correctly, clients must access a domain-based DFS namespace by using the format \\DomainName\RootName, not \\RootServerName\RootName.