Windows 7 / Networking

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The Distributed File System

To improve the reliability and availability of file shares in an enterprise network, Microsoft has developed the Distributed File System (DFS). DFS improves file share availability by providing a single, unified namespace to access shared folders hosted across one or more servers. A user needs to only remember a single server or domain name and share name to connect to a DFS shared folder.

DFS has many benefits and features that can simplify data access and management from both the administrator and end-user perspective. DFS provides three main functions, as follows:

• Data redundancy: DFS can provide access to a single share that is hosted on multiple servers. This allows clients to get referred to or fail over to a different server if the primary server cannot be contacted.
• Automated data replication: DFS can be configured to utilize the Distributed File System Replication (DFSR) service, and can be configured to automatically synchronize folders between DFS servers to provide data redundancy or centralized storage of branch office data.
• Distributed data consolidation-DFS can be used to provide a single namespace that can contain several distinct or unique data sets, which can be hosted on separate servers. This enables administrators to provide access to existing file shares hosted on many different file servers, from the single namespace, without adding replication or redundant data sets.

DFS Namespaces

DFS can be used in a few different ways, but it will usually require the creation of a DFS namespace. A DFS namespace can be the name of a single server and share folder or the DNS and NetBIOS name of an Active Directory domain and share folder. The DFS namespace is also referred to as the namespace root. The namespace allows connections to automatically be redirected to different servers without user knowledge. For example, when a client connects to the domain DFS namespace named \\Companyabc.com\Apps, the client will be redirected to \\Server10\Apps, and the client will be unaware of this redirection.

For DFS to function properly with regard to client redirection and just basic connectivity, a compatible DFS client is required. In a network that supports different versions of Windows, Apple Mac, and UNIX clients, DFS should be tested on all clients before it is released to production. DFS-compatible clients are currently available for the following Microsoft Windows operating systems:

• Windows 2000 Professional and Server.
• Windows XP Professional.
• Windows Server 2003 and Windows Server 2003 R2.
• Windows Vista Business, Ultimate, and Enterprise.
• Windows 7 Professional, Ultimate, and Enterprise.
• Windows Server 2008 and Windows Server 2008 R2.
• Windows NT Server and Workstation 4.0 with Service Pack 6a and the Active Directory Client Extension found on the Windows 2000 Server CD.
• Windows 98 can support DFS domain namespaces with the installation of the Active Directory Client Extension found on the Windows 2000 Server CD.

Because DFS clients do not connect to the actual server by name, administrators can move shared folders to new servers and user logon scripts and mapped drive designations never need to be changed. In fact, DFS data presented in a single namespace can be hosted on multiple servers to provide redundancy and distribution of large amounts of data.

Standalone DFS Namespace

A standalone DFS namespace utilizes the name of the server hosting the DFS namespace. Standalone DFS namespaces should be used when file system access needs to be simplified and the amount of data exceeds the capacity of a single server. Also, if no Active Directory domain exists, a standalone DFS namespace is still supported. When a standalone DFS namespace is created on a Windows Server 2008 R2 server that is a member of an Active Directory domain, DFS replication can be configured.

Domain-Based DFS Namespace

A domain-based DFS namespace utilizes the name of the Active Directory domain the DFS namespace server is a member of. A domain-based DFS namespace is created upon deployment of an Active Directory domain at the location of \\domain\SYSVOL to replicate the domain group policies and logon script folders. Domain-based DFS namespaces support replication using either the File Replication Service or the new Distributed File System Replication service.

Domain-Based DFS Namespace Windows 2008 Mode

When a new domain-based DFS namespace is created on a Windows Server 2008 R2 system, an option to enable Windows Server 2008 mode is presented. This option is available on Windows Server 2008 and Windows Server 2008 R2 systems when the namespace is hosted on either operating system, and the domain the system is a member of must be running in Windows Server 2008 domain functional level and at least Window Server 2003 forest functional level. This means that the domain must have only Windows Server 2008 domain controllers and the entire forest must have only Windows 2003 and/or Windows 2008 domain controllers.

Windows Server 2008 mode enables the namespace to contain more than 5,000 DFS folders and it also enables access-based enumeration within the DFS namespace. Historically, many organizations ran into issues when deploying DFS because over time, the number of folders beneath a namespace grew too large and they had to create multiple namespaces and segregate the data, which in some cases defeated the purpose for deploying DFS. Windows Server 2008 namespace mode surpasses this previous limitation and with the added bonus of access-based enumeration, it allows for users to locate the data that is relevant to them much easier.

It is important to note that the same functionality enabled for a Windows 2008 mode domain-based namespace exists on standalone DFS namespaces when the namespace server is hosted on a Windows Server 2008 R2 server, so this functionality can be leveraged immediately, even in organizations that are far from meeting the requirements for Windows 2008 mode domain-based namespaces.