Introduction to Dfs

Limits of Dfs 260 characters per file path 32 alternatives per volume 1 Dfs root per server Unlimited Dfs roots per domain Volumes limited by system resources

Overview of Dfs Roots The Dfs Service is auto-installed with the installation of Microsoft Windows 2000 Server. Two types of Dfs roots can be configured on Windows 2000 Server computers: stand-alone and domain.

Stand-Alone Dfs Roots Stand-alone Dfs information is stored in the local registry. A stand-alone Dfs root permits a single level of Dfs links. When the Distributed File System snap-in is used to connect to existing stand-alone Dfs roots, all servers known to the browse list are retrieved because there is no unique NetBIOS name registered by Dfs-enabled servers. Stand-alone Dfs roots can be located on all supported file systems, although locating resources on NTFS-formatted partitions is recommended. Stand-alone Dfs roots offer no replication or backup; the Dfs root represents a single point of failure.

Domain Dfs Roots Multiple servers hand out referrals for the Dfs namespace. A fault-tolerant Dfs root is stored in Active Directory services and is replicated to every participating Dfs root server. Changes to a Dfs tree are automatically synchronized with Active Directory services. Fault-tolerant roots must be located on NTFS version 5.0– formatted partitions. The list of domains and servers is populated by querying the global catalog for all fault-tolerant Dfs roots. Dfs replication topology uses the existing Active Directory replication topology.

Configuring a Stand-Alone Dfs Root Stand-alone Dfs stores the Dfs topology on a single computer and does not provide fault tolerance. A stand-alone Dfs root is physically located on the server that users initially connect to. To create a stand-alone Dfs root, use the Distributed File System snap-in to start the New Dfs Root wizard.

Creating a Stand-Alone Dfs Root

Configuring a Domain Dfs Root Domain Dfs writes the Dfs topology to the Active Directory store, which allows links to point to multiple identical shared folders for fault tolerance. Domain Dfs supports DNS, multiple levels of child volumes, and file replication. To create a domain Dfs root, use the Distributed File System snap-in to start the New Dfs Root wizard.

Configuring New Dfs Links Users can browse folders under a Dfs root without knowing where the referenced resources are physically located. After you create the Dfs root, you can create Dfs links. To create a Dfs link, use the Distributed File System snap-in to open the Create A New Dfs Link dialog box.

Creating a Dfs Link

Dfs Links

FRS Replication FRS is installed automatically on all Windows 2000 Server computers. FRS is configured to start automatically on all domain controllers and manually on all stand-alone and member servers. The Active Directory store uses FRS to synchronize the directory among all the domain controllers. Active Directory services automatically generates a ring topology for replication among domain controllers in the same domain. The ring structure ensures that there are at least two replication paths from one domain controller to another.

Site and Domain Structures A site is made up of one or more IP subnets that identify a group of well-connected computers. Domain structure and site structure are maintained separately in Active Directory services. A single domain can include multiple sites, and a single site can include multiple domains.

Single Domain with Single Site

Single Domain with Multiple Sites

Multiple Sites with Multiple Domains

Intra-Site Replication Intra-site replication occurs between domain controllers within a site. Replicated data is not compressed. The default replication interval is five minutes. Replication is trigger-based (notification and pull).

Inter-Site Replication Inter-site replication occurs between domain controllers in different sites. You can specify the time when inter-site replication should occur. The default replication interval is three hours. You can specify the network transport for use in inter-site replication. Inter-site replication is compressed, regardless of the transport used. Inter-site replication compression reduces the data on the network by 88 to 90 percent. Inter-site replication is not configured automatically; it must be configured by an administrator.

Knowledge Consistency Checker (KCC) The KCC generates a ring topology for replication among domain controllers in the same domain. The ring structure guarantees that there are at least two replication paths from one domain controller to another. The KCC analyzes the replication topology within a site to ensure that the replication topology is efficient.

Unique Sequence Numbers (USNs) When a directory object is updated at a domain controller, a USN is assigned. When the domain controller writes the change into the directory, it also writes the USN. Each domain controller maintains a table of the USNs that it receives from every other domain controller in the domain. USNs eliminate the need for precise time stamps for changes. USNs simplify recovery after a failure.

Replicating SYSVOL Changes to the %systemroot%\SYSVOL folder on any domain controller are automatically replicated to other domain controllers within the site. The replication topology and process are separate but identical to Active Directory replication. Windows 2000 Server sets up a default folder structure for SYSVOL.

Replicating Dfs Fault-Tolerant Roots Dfs and file replication support a number of features. Each Dfs root or link can reference a replicated set of share consequences. Dfs replication is disabled by default; use the Distributed File System snap-in to enable replication.

Configuring FRS for Inter-Site Replication Use the Active Directory Sites And Services snap-in to configure inter-site replication. To configure the FRS settings, you must create a new site link for the inter-site transport protocol listed in the console tree.