Nomenclature

These are the key terms that are associated with Dfs:

Dfs topology . Overall logical hierarchy of a distributed file system, including elements such as roots, links, shared folders, and replica sets, as depicted in the Dfs administrative console. This is not to be confused with Dfsnamespace , ** which is the logical view of shared resources seen by users.

Dfs root . The share at the top of the Dfs topology that is the starting point for the links and shared files that make up the Dfs namespace. A Dfs root can be defined at the domain level for domain-based operation or at the server level for stand-alone operation. Domain-based Dfs can have multiple roots in the domain but only one root on each server.

Root replica . The server that duplicates a Dfs root to provide greater availability. The server that is hosting the Dfs root is responsible for handing out referrals to clients for shared folders. If that server becomes unavailable and a root replica has not been created, the Dfs namespace becomes inoperative. Replicas can also be created for existing Dfs links.

Dfs link . Part of the Dfs topology that lies below the Dfs root and forms a connection to one or more shared folders or another Dfs root. It does this by mapping a DNS name to the standard UNC of the target shared folder.

Dfs shared folder . Files or folders in the Dfs namespace that are shared by users with proper permissions. Shared folders can exist at the root level (domain-based Dfs only) or be referred to by Dfs links.

Replication policy . Configuration rules that enable automatic replication of files between computers where replication has been enabled. Replication is supported on the root and child folders of domain-based Dfs. A stand-alone Dfs cannot take advantage of automatic replication because it does not use Active Directory. The replication policy can be different for each replica set in the Dfs namespace.

Partition knowledge table (PKT) . A table that maps root and replica nodes in the Dfs namespace to Active Directory sites and physical servers. For a domain-based Dfs root, the PKT is stored in Active Directory and made available to each domain controller in a domain. For a stand-alone Dfs root, the PKT is stored in the individual server's registry. When a Dfs client gains access to a shared folder in the Dfs namespace, it caches that portion of the PKT for the length of time specified in the TTL.

Referral . The referral is the physical server and share residing in the PKT that clients connect to.

Time-To-Live (TTL) . The length of time that a Dfs client stores the referral information from the PKT when it accesses a shared folder. Dfs clients request a new portion of the PKT when the TTL expires or when the client is restarted. The TTL resets if the shared folder is visited before expiration. It is configurable on a per-link basis.

Revision level . Refers to Dfs client compatibility. There are three revisions of Dfs clients that can be viewed in Network Monitor traces. Clients that are running Windows NT version 4.0, Windows 98, and Windows 95 support Dfs revision level 2; clients that are running Windows 2000–based support revision level 3. Version 1 clients do not exist. Dfs clients and servers negotiate the highest common protocol revision supported.

A few of the terms in the version of Dfs included in Windows NT 4.0 were renamed in Windows 2000. Table 17.2 shows a list of these terms and their replacements.

Table   17.2 Dfs Nomenclature Map

Dfs in Windows NT 4.0	Dfs in Windows 2000
Alternate volume	Replica
Child node, junction, inter-Dfs link	Dfs link
Fault-tolerant Dfs	Domain-based Dfs
Dfs volume, leaf, branch	Shared folder