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.