Microsoft has made many improvements to the Distributed File System (DFS) in Windows Server 2003 R2 that make it a much more attractive feature for Windows system administrators. At the same time, the DFS terminology used in R2 has also changed. Here's a rundown of the new terms, as well as what you need to know about them.
Namespace root (formerly DFS Root) provides the "starting point" of a DFS environment; the term is also used to refer to the DFS environment as a whole. A namespace root can have one or more namespace targets (formerly root targets), which are physical servers that host the configuration information for a particular namespace. In our example, \\company.com\shared is a namespace root. On each namespace target, DFS creates a physical folder that corresponds to the name of the namespace root.
DFS namespace refers to the overall "view" of a DFS environment as it appears to the user. You can create one of two types of DFS namespaces: a domain-based namespace or a standalone namespace.
A domain-based namespace is published to Active Directory (AD) and supports the file replication and fault tolerance features. A standalone namespace stores its configuration information in the Registry of the namespace target that hosts it. Standalone namespaces do not integrate with AD. A domain namespace can have multiple namespace targets configured for the same namespace, with the configuration information for the namespace replicated to each domain root as a part of AD replication. A standalone namespace can only have a single namespace target configured
DFS folder (formerly DFS link) is the portion of the DFS namespace that maps to a link target. In the example used in my previous article on DNS, \\company.com\shared\training is a DFS folder. On each namespace target, there's a physical folder created that corresponds to the name of the DFS folder. This is a reparse point used by Windows to redire
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ct the client to the appropriate location. If a user tries to access this folder directly, they'll receive an error.
Note: When planning for DFS scalability, Microsoft recommends that you configure no more than 5,000 DFS folders within a domain-based namespace, or up to 50,000 within a standalone namespace. The limitation for domain-based namespaces is designed to limit the space being taken up by DFS configuration information within the AD database.
DFS folder target (formerly DFS link target) refers to the physical location that a DFS folder points to. The \\fs1\training share is the folder target of the \\company.com\shared\Training DFS folder. In a domain-based namespace, you can configure a single DFS folder to point to multiple folder targets and the DFS service will replicate changes between the different physical locations.
DFS referrals is the process that DFS uses to take a DFS link submitted by a client and to point (refer) them to the correct physical server. A little-known feature of DFS is that referrals can be enabled or disabled for a particular link without actually deleting the link. This is particularly useful if you have multiple folder targets defined for a particular folder and you need to bring one of the targets offline for maintenance. Rather than allowing DFS to continue to refer clients to the offline server, creating an error for the user, you can temporarily configure DFS to refer clients to only those link targets that are still operational.
DFS referrals are also site-aware, meaning that if a DFS folder has folder targets in multiple cities, DFS will refer any connecting clients to the closest folder target based on the sites and subnets configured in AD.
About the author: Laura E. Hunter (CISSP, MCSE: Security, MCDBA, Microsoft MVP) is a senior IT specialist with the University of Pennsylvania where she provides network planning, implementation and troubleshooting services for business units and schools within the university. Hunter is a two-time recipient of the prestigious Microsoft "Most Valuable Professional" award in the area of Windows Server-Networking. She is the author of the Active Directory Field Guide (APress Publishing).
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