DFS Replication

When an Active Directory domain exists, standalone and domain-based DFS namespaces support the replication of DFS data stored on multiple servers. This can be a valuable tool used to distribute company applications to each site or to provide centralized storage of remote office data for redundancy, centralized backup, and to support users who travel and work in different offices.

With the release of Windows Server 2003 R2 and further improved in Window Server 2008 R2, a service to extend the functionality and optimize DFS Replication has been created. This service is called the Distributed File System Replication (DFSR) service, which utilizes the new Remote Differential Compression (RDC) protocol. DFSR replaces the legacy File Replication Service (FRS) that was previously used to replicate DFS data. As long as all of the DFS servers defined in a DFS replication group are running Windows Server 2003 R2 or later, the DFSR service will be used to replicate the data. If any of the systems are running a previous version operating system, DFS data will be replicated using the File Replication Service. There is one exception to this rule: The Domain System Volume (SYSVOL) will be replicated between domain controllers using the File Replication Service, even if all the domain controllers are running Windows Server 2008 R2, until the domain functional level is raised to the Windows Server 2008 level and the SYSVOL is migrated from FRS to DFSR.

DFS Replication and DFS namespaces are independent of one another, but they can be used together, as they are commonly deployed in this fashion. Replication of folders can be set up between servers that do not host any DFS namespaces or namespace folders but the DFS Replication service must be installed on all systems participating in the replication. Windows Server 2008 R2 increases DFS Replication security and performance because all DFS Replication is compressed and encrypted. Note that the data stream cannot be set to run unencrypted.

DFS Terminology

To properly understand DFS, a number of technical terms are used when deploying, configuring, and referencing DFS. Although the DFS namespace and DFS Replication have already been described, the remaining terms should also be understood before reading the remainder of this tutorial or deploying a new DFS infrastructure:

• DFS namespace: A unified namespace that presents a centralized view of shared folder data in an organization.
• DFS namespace server: A Windows server that hosts a DFS namespace.
• DFS namespace root: The top level of the DFS tree that defines the namespace for DFS and the functionality available. The namespace root is also the name of the DFS namespace. A domain-based root adds fault-tolerant capabilities to DFS by allowing several servers to host the same DFS namespace root.
  NOTE: Depending on which Server version, service pack, and edition of Window Server 2003 or 2008 is used will determine how many namespaces are supported on a single server. Please refer to online Microsoft documentation to determine which edition is right for your organization's implementation of DFS.
• DFS folder: A folder that will be presented under the root when a DFS client connects. When a root is created, folders can be created within the file system, but DFS folders allow the system to redirect clients to different systems other than the namespace server hosting the root.
• Folder target: A shared folder hosted on a Windows server. The DFS folder name and the share name do not need to be the same but for troubleshooting purposes it is highly recommended. Multiple folder targets can be assigned to a single DFS folder to provide fault tolerance. If a single folder target is unavailable, clients will be connected to another available target. When DFS folders are created with multiple folder targets, replication can also be configured using DFS replication groups to keep the data across the targets in sync. Folder targets can be a share name or a folder beneath a share. For example, \\server1\userdata or \\server1\userdata\Finance are both valid folder targets.
• DFS tree: The hierarchy of the namespace. For example, the DFS tree begins with the DFS root namespace and contains all the defined folders below the root.
• Referrals: A configuration setting of a DFS namespace and/or folder that defines how DFS clients will connect to the namespace server, a folder in the namespace, or a particular folder target server. Referral properties include limiting client connections to servers in the local Active Directory site and how often to check the availability of a DFS server. Disabling a target's referral keeps it from being used by clients. Target referral can be disabled when maintenance will be performed on a server.

DFS Replication Terminology

DFS uses either the File Replication Service or the Distributed File System Replication service to automatically replicate data contained in DFS folder targets. To understand the replication concepts, you must understand some key DFS replication terminology. Here are some important terms:

• Replication: The process of copying data from a source server folder to a destination server folder.
• Replication connection: The directory object that defines and manages the replication between a sending and receiving replication member server. The replication connection defines the replication schedule, which service will replicate the data, the sending and receiving members, and any bandwidth restrictions for the connection. Each replication connection has only a single sending and receiving replication member.
• Replication member: A server that shares a common replication connection. The receiving replication server receives data from a sending member server specified in the replication connection. The sending replication partner sends data to the receiving member specified in the replication connections.
• Read-only replication folders: Windows Server 2008 R2 introduces support for read-only replicas. This can be useful for auditing, centralized backup, or managing data sets. Only the replication members that are not defined as the primary source can host read-only replication folders. Read-Only Domain Controllers host the SYSVOL as a read-only replication folder. When read-only replication folders exist, it is a best practice to ensure that replication is only one-way to the read-only replication folder.
• Replication group: All the servers, folders, and connections that define a replication set of data.
• Multimaster replication: This defines two-way replication between multiple servers in a replication group. With multimaster replication, data changed on any server in the group will be replicated to every other server in the group.