Abstract
This chapter discusses the installation and configuration of the Distributed File System (DFS), which enables you to centralize network file system resources into a single logical location. The author walks you through the installation of DFS and explains the configuration of DFS volumes.
In this chapter, I discuss the installation and configuration of the Distributed File System (Dfs). The Distributed File System enables you to centralize network file system resources into a single logical location. Dfs abstracts the distributed network file system resources into a unified location, and allows a degree of load balancing for file system resources.
INTRODUCING THE DISTRIBUTED FILE SYSTEM
The Microsoft Distributed File System (Dfs) provides the capability to logically centralize the physically distributed file system resources on your network. Using Dfs, you can represent a collection of file system resources as unified, even when they reference resources located on other network servers. Dfs enables you to create a single logical structure in which you specify volumes that are actually distributed across multiple physical locations and servers. You can even combine resources from servers using different file systems and running operating systems other than Windows NT, such as NetWare, into a single Dfs volume.
Dfs increases the availability of important network resources by providing organized access to resources distributed around the network. Using Dfs, an administrator can build a Dfs volume containing all the data that is relevant to a particular organization and network clients can access that volume as if it were a single, extremely large hard disk.
The logical organization of file system resources provided by Dfs enables you to grow or modify your network with a minimum of disruption to network users. If the physical location of a resource changes, you only have to change one reference on the Dfs server for the share to remain accessible to network clients.
As an administrator, you can leverage Dfs to centralize the management of IIS file system resources and enhance services such as the Web, FTP, and Index Server. You can also use Dfs to provide a collection of data/drives to streamline network maintenance (virus scanning, backups, and so on).
The Distributed File System runs as a network service and is managed through both a control panel and its own administrative tool, the Dfs Administrator. The network Control Panel enables you to configure the root Dfs volume. All other administration, including creation and management of the leaf volumes, is done with the Dfs Administrator.
Two types of volumes are employed by the Distributed File System:
Dfs root volume is a share on the NT Server running the Dfs service that acts as the top-level directory of the file system resources represented on the Dfs volume. Only NT Server can host Dfs roots, and currently you can have only one root Dfs volume per server. This limitation is expected to be changed in Windows NT 5.
Leaf volumes can be hosted on NT Server, NT Workstation, Windows 95, Windows 98, and NetWare. Volumes on Windows NT can be either NTFS or FAT. Dfs leaf volumes on NT Workstation are still limited to ten user connections. You will want to keep this in mind if you are planning on using file system resources on computers running NT Workstation.
The structure of a Dfs tree is limited to the two levels of volumes (root and leaf); however, you can nest a Dfs tree inside another Dfs tree, providing a way for multiple Dfs root volumes to be linked together within a Dfs tree. This linkage is transparent to clients. The volumes that provide the point for the linkage are called inter-Dfs links, or junction points. Only NT Server can host inter-Dfs connections, and only a single level of nesting is permitted. Later versions of Dfs will provide the capability of nesting many more layers of Dfs volumes.
This nesting of Dfs trees is a powerful mechanism for organizing your network resources. For example, each major department of an enterprise (HR, admin, and so on) might create its own Dfs volumes that hold all of that department’s resources. Project groups may also want to create a Dfs volume to centralize the resources being used in their work. A network administrator might then create a Dfs volume that contains all the departmental Dfs volumes, and use it for administrative tasks.
The Dfs root volume can also use the directory structure within the local file system to provide additional structure and organization for the Dfs volume. You can insert a Dfs leaf volume at any point in the directory path, with these provisions:
You can only insert a leaf volume into the Dfs root volume or a directory that exists underneath that physical directory.
A link to an external Dfs root volume must be a child of the root of the host Dfs tree, not in a subdirectory.
Note: Any volume that is located on a system other than Windows NT Server 4.0 or above (such as NT Workstation or NetWare) is considered a down-level volume. Although down-level volumes can be published in the Dfs tree, they cannot host a Dfs root volume or serve as an inter-Dfs junction.
Dfs also enables you to specify multiple storage points for a volume, providing the means to distribute the volume location to multiple NT servers. By distributing frequently accessed or critical data to multiple servers, you can improve network performance and provide a degree of fault tolerance for those resources. Up to 32 alternative volumes (or replicas) can be assigned for a single volume.
Dfs volumes are accessible by NT Workstation 4.0 and 98 networking clients, and can be accessed by Windows 95 clients with the provided client software. With few exceptions, if a client can access a file share directly, it can access that same file using Dfs. However, Windows 95 can only take referrals to SMB volumes, so NetWare volumes can only be accessed by Windows 95 clients via MS Gateway Services for NetWare.
From the perspective of a network client, a Dfs directory tree functions as a standard Windows NT network share. Clients accessing the Dfs volumes are not required to know the server name to which they are connecting in order to access the volume. Once network clients connect to a Dfs tree, they can access the file resources within the tree without specifying the server physically hosting the file system resources. The Dfs client uses client-side caching of Dfs tree information to enhance performance and to provide a mechanism for quick recovery from lost connections.
When network clients access a Dfs share that has multiple copies, they are provided with a list of all the replicas of that data. From this list, the client arbitrarily selects a server to contact for that session. The information about other access points for that Dfs resource is cached to provide a more robust file service. If the connection fails, the Dfs client selects another server from the list and establishes a connection, without user intervention.
Security while using Dfs is transparent to the client. Dfs does not implement security mechanisms; rather, it only passes through existing share or file access permissions. Existing permissions assigned to the Dfs volume, the network share, and the specific files will apply to client requests. The only time Dfs handles client security credentials is when establishing a connection to another Dfs root while traversing an inter-Dfs link. This mechanism is explained in the “Connecting to a Dfs Share” section of this chapter.
OBTAINING AND INSTALLING DFS
Dfs is an add-on software component for NT Server 4.0 that provides the Dfs service and Dfs Administrator tool. Dfs client software is also available for Windows 95, and supports Dfs operations on Windows 95 clients.
Microsoft’s Distributed File System programs (client and server) can be downloaded from the BackOffice Download and Trial Center at the following URL:
http://www.backoffice.microsoft.com/downtrial
From the list at the Download and Trial Center, select the Microsoft Distributed File System.
Alternatively, you can go directly to the Dfs Web page at the following URL:
The installation of Dfs requires that the host server be running build 1381 or later of Windows NT 4.0; also, Service Pack 3 must be installed.
To begin the Dfs installation, double-click the Dfs _v41_ i386.EXE file and follow these steps:
You are first presented with a licensing agreement dialog box. Click Yes to continue the installation.
You are then presented with a Welcome to Setup dialog box, explaining that setup will copy Dfs files into the %systemroot%\system32\Dfs directory, and informing you that you will need to install Dfs from the Network Control Panel before configuring and using Dfs. Press Continue to proceed with the installation of Dfs.
The file-copying portion of the Dfs installation finishes and presents you with a dialog box confirming the file copy. Press Exit to continue and view the Dfs release notes.
The Dfs release notes are displayed in a Wordpad document, and contain summary information regarding what’s in this release of Dfs and the basics of installing Dfs onto the server or Win95 clients. For detailed information on Dfs, read the online Administrators guide contained in the Dfsdoc.htm file located in the %systemroot%\system32\Dfs\docs directory.
Installation of Dfs must be continued through the Network Control Panel, which adds Dfs as a network service. To continue the Dfs installation, click Start Settings Control Panel.
Double-click the Network Control Panel.
Select Services Add Have Disk.
In the Insert Disk dialog box that appears, enter the path to the Dfs files you just extracted to the %systemroot%\system32\Dfs directory (for example, d:\nt\system32\dfs).
You are presented with a select OEM option dialog box showing the distri-buted file system software, as shown in Figure 25-1. Click OK to continue installing Dfs.
The Dfs installation process then provides you with the option to host Dfs on a share, as shown in Figure 25-2. By default, the checkbox for this option is not selected. To create the root volume of the Dfs tree, click the checkbox, and either specify an existing share or create a new share for Dfs.
Note: This Configure Dfs dialog box is also available from the Network Control Panel Properties by selecting Distributed File System Properties in the Services property sheet. You can use this dialog box to create a new Dfs root volume. When you create a new share, this effectively changes the location of the Dfs root volume and renders the previous volume inaccessible (because only one root volume can be operating on a server at a time).
To create the share, click New Share. In the New Share dialog box, shown in Figure 25-3, enter the name of the directory to share, or use Browse to select the directory for the Dfs share. Once you have selected the directory for Dfs, click Create Share to continue.
If the directory selected doesn’t already exist, you are prompted to create it. Click Yes to create the directory for the Dfs share.
If this is a new share on the system, you are then prompted to share the directory, as shown in Figure 25-4. Click the radio button next to Shared As, supply the share name for the Dfs share, and set permissions as needed. Click OK to return to the Configure Dfs dialog box, and click OK again to continue the installation.
At this point, focus is returned to the Network Control Panel services tab. Click Close to continue. The network settings change dialog box appears, prompting you to restart your computer. Verify that all data is saved and that applications are closed, then click Yes to restart your computer.
ADMINISTERING DFS VOLUMES
Once the system has rebooted, you can start building the structure of your Dfs tree and adding file system resources to the Dfs volume. To administer the Dfs tree, you must be logged on to the NT Server using the NT Administrator account, or an account with Administrator privileges. The Dfs installation program makes multiple additions to the Start menus, adding a Dfs administration tool as well as a Dfs group.
The Dfs Administrator is added to the Administrative Tools (Common) submenu. The remaining Dfs options are added to the Start Programs Distributed File System menu, and contain links to the Dfs directory, the Dfs Admin Guide, and Readme.
The contents of the Dfs program directory can be accessed by clicking Start Programs Distributed File System Dfs Directory.
Dfs volumes can be managed using either the Dfs Administrator or the DFSCMD.EXE command-line utility. The command-line utility provides support for addition and removal of Dfs volumes and replica servers.
Using the Dfs Administrator
Most of the administrative functionality for Dfs is provided by the Dfs Administrator program. The Dfs Administrator even provides the capability to invoke Windows Explorer to access the file system resources referenced by your Dfs tree.
Activate the Dfs Administrator by clicking Start Programs Administrative Tools (Common) Dfs Administrator. The Dfs Administrator has three menus, as shown in Figure 25-5: Dfs, View, and Help.
The Dfs menu contains nine items that enable you to manage Dfs servers and volumes, as shown in Figure 25-6: Select Dfs, Open, Explore, Add to Dfs, Remove From Dfs, Properties, Load, Save As, and Exit.
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