Distributed File System

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Distributed File System
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Author:	Beth Sheresh Doug Sheresh Robert Cowart
Published:	April 1999
Copyright:	1999
Publisher:	IDG Books

Managing Dfs Servers
To choose a Dfs server to administer, click Dfs

Select Dfs. You are presented with the Select a Dfs dialog box, as shown in Figure 25-7. Dfs queries for Dfs servers on the network within the current domain, and enables you to select the one you want to manage.

Dfs servers outside the domain are not displayed, but can be accessed by entering the server name. For example, to access a Dfs server that is not displayed in the dialog box, type the name of the server (for example, “phoenix”) and click OK. The Dfs administrator switches to the specified Dfs server and displays the volumes managed by that server’s Dfs configuration, as shown in Figure 25-8.

Managing Dfs Volumes
The Open and Explore options on the Dfs menu will open a window or Explorer view (respectively) on the currently selected Dfs volume. (This is useful for performing normal file maintenance.)

From here, you can add a leaf volume. To add a Dfs Leaf Volume, follow these steps:

To specify additional Dfs path maps that will be accessed via this Dfs volume, click Dfs Add to Dfs.
To create a new path map, enter the name for the shared file resource and the UNC (\\server\share) for the network path where the resources are located, as well as the comment or description to be displayed, as shown in Figure 25-9.
The Dfs administrator is updated to reflect the new Dfs volume, as shown in Figure 25-10.

When you remove a Dfs volume, it does not delete any files on the physical volume referenced by the Dfs share, just the logical reference to that location maintained by Dfs. To delete a Dfs volume, highlight the specific Dfs volume to be deleted, and press the delete key or select Dfs

Remove From Dfs. When you delete a Dfs volume, the message shown in Figure 25-11 appears.

A root Dfs volume can contain other references to other Dfs root volumes as leaf volumes, thus enabling you to nest layers of volumes in a multilevel tree. In addition to the network resources in the Dfs tree, you can specify local directory locations for storage and organization. To nest a remote root Dfs volume, create a volume and specify the remote Dfs volume network location (in UNC format).

Using Multiple Dfs Servers for a Volume
A Dfs volume can reference multiple server locations as the repository of the volume contents. Using multiple server locations for data files enables you to distribute the load to multiple servers, increasing server responsiveness and availability of data.

Although Dfs allows you to have multiple servers supporting each logical Dfs volume, it does not synchronize the data between the servers. Synchronization of server data must be performed by operations outside of Dfs, such as the Windows NT Server 4.0 Directory Replicator service or other synchronization tools or methods. (Further information on the NT Directory Replicator service is available in the Windows NT Server Resource Kit.).

To specify directories on multiple servers for a Dfs volume, follow these steps.

Right-click the volume in the Dfs Administrator and select Properties.
The Properties menu option displays the Dfs volume information, as shown in Figure 25-12, and enables you to add another Dfs server for the specified Dfs volume.
Click Add to add another server for the selected Dfs volume. The Add Server dialog box is displayed, as shown in Figure 25-13. You can enter the server name and path, or use the Browse button to select a server.
Click Browse to select a location on your network as the additional location for the Dfs volume contents. The Browse for Folder dialog box, shown in Figure 25-14, prompts you to select the server and directory to mount for the Dfs volume.
When you instruct Dfs to add another server for a Dfs volume, the message shown in Figure 25-15 is displayed, and you are informed that requests for this resource will be distributed among all file servers for this Dfs volume. Because no automatic synchronization of contents is provided, you may want to provide read-only access for most users.
The Dfs administrator is updated to reflect that there are multiple servers supporting the selected Dfs volume, as shown in Figure 25-16. To view the list of assigned server/share locations, right-click the volume, click properties, and select the server/share in the drop-down list.

Saving and Loading Dfs Information
The Dfs Save As and Load options enable you to save and load (respectively) Dfs configuration information. Storing backups of your Dfs configuration files provides a way for you to quickly restore a Dfs share. This information is stored in a comma separated value (.CSV) file. With most text editors, a .CSV file can easily be modified to reflect different root servers.

The format of the .CSV file is shown as follows:

   1
   \\DRAGON\resource
   Name,Storage,Comment
   \\DRAGON\resource,\\DRAGON\resource,Dfs Root Volume
   \\DRAGON\resource\html,\\unicorn\z$\html;\\unicorn\c$\html,HTML
   Resources

Note: The Dfs server and root volume referenced by this file must match the name of the server it is being loaded on, as well as the value set in the Network Control Panel

Services

Dfs as the share to host Dfs.

Viewing and Filtering Dfs Volumes
The Dfs view menu has five options: Toolbar, Status Bar, Filter, Font, and Refresh, as shown in Figure 25-17. The Toolbar and Status Bar options toggle their respective displays, and Refresh updates the Dfs display. View

Font enables you to select the font used by Dfs Administrator.

View

Filter enables you to filter the list of volumes displayed in Dfs Administrator. Although the default is to show all volumes, you can filter lists of volumes by what the name contains, by what the comment contains, and by the volumes that have multiple servers, as shown in Figure 25-18.

Using Dfs at the Command Line
You can use DFSCMD.EXE to configure Dfs from the command line. You can create and remove volumes, add or delete a replica server, and view existing volumes. All command line operations use UNC pathnames to specify the Dfs and network shares.

In the list below, the parameter (for example, /map) and description for each of the Dfs command line options precede the example syntax used to perform that operation:

/map—Establishes a Dfs volume path, mapping the Dfs volume to a network share.

DFSCMD /map \\DfsSvr\Share\Path \\Server\Share\Path

/unmap—Enables you to remove a Dfs volume (and references to replicas).

DFSCMD /unmap \\DfsSvr\Share\Path

/add—Enables you to add a replica server to the specified Dfs volume.

DFSCMD /add \\DfsSvr\Share\Path \\Server\Share\Path

/remove—Enables you to remove a replica server from the specified Dfs volume.

DFSCMD /remove \\DfsSvr\Share\Path \\Server\Share\Path

/view—Enables you to view all Dfs volumes on the specified server.

DFSCMD /view \\DfsSvr\DfsShare [/partial | /full]

USING DFS CLIENTS

The Dfs client is part of Windows NT 4.0 and Windows 98, and a Dfs client is available for Windows 95. Windows 95 does not natively support Dfs, and requires installation of a client component to access Dfs volumes. Dfs client components are built into Windows 98 and Windows NT 4.0, so no specific installation or configuration needs to be done to allow these operating environments to access Dfs volumes.

Once the Dfs client is installed, its use is transparent to the user accessing the Dfs volume. When a Dfs path is specified, the Dfs client retrieves the information regarding the associated physical location of the resources from cache or the Dfs server. The network request is then redirected to that location.

The Dfs client operates in essentially the same manner on all Windows platforms. However, there are minor differences you should be aware of between the various versions:

The Windows 95 Dfs client has two limitations: it is unable to access leaf volumes on non-SMB network servers (such as NetWare), and DNS namespace support is not provided.
The Windows NT client allows the mapping of a network drive to a \\server\share\directory path (rather than only \\server\share), with the net use command.

Windows 95 does not ship with a Dfs-aware network client, and a specific add-on must be installed on Windows 95 systems for them to be able to access Dfs volumes. The Dfs server distribution package from Microsoft includes the Windows 95 client software, which is installed on the server as part of the Dfs installation.

You can get the Windows 95 client component for Dfs separately at the following URL: http://www.microsoft.com/ntserver/nts/downloads/winfeatures/NTS DistrFile/default.asp If you download the stand-alone Windows 95 client, it is installed in a two-step process:

First, the downloaded file must be executed on the client, extracting its contents to the %windir%\system\Dfs directory.
Once you have extracted the Dfs client component, proceed with the installation by following the client installation instructions in the next section.

No Dfs client software needs to be installed for Windows 98 and Windows NT 4.0, because the retail releases of both ship with a Dfs-aware network client. However, the Windows NT Service Pack 3 or greater is required for NT systems that operate as Dfs clients. If SP3 or greater is not installed, the client may encounter access error conditions.

Installing the Windows 95 Dfs Client
To install the Dfs client for Windows 95, it must already be extracted onto your Windows NT Server 4.0 or Windows 95 client machine. The Dfs client for Windows 95 is located on your NT server in the %systemroot%\system32\Dfs\Win95 directory, which must be shared and accessible to your Windows 95 clients.

To install the Dfs client components for Windows 95, follow these steps:

On the Windows 95 client system, click Start Settings Control Panel.
Double-click the Network Control Panel.
Click Add Service Have Disk
In the Install From Disk dialog box, enter the UNC location (for example, \\server\share) of the shared directory on the NT Server containing the Dfs client component, or the %windir%\system\Dfs directory if you’re installing from the client machine.
Select the displayed DFS Services for Microsoft Network Client, as shown in Figure 25-19, and click OK.
You are prompted for files from the Windows 95 CD. Specify the drive and directory containing the Windows 95 CD files, and click OK.
A message is displayed stating that you have to reboot the Windows 95 system. Click OK to reboot.

Accessing Dfs Volumes
Once Dfs is installed on the Windows 95 client, Dfs volumes can be accessed in the same way as any other network share, as shown in Figure 25-20. When you access a network share, the request is redirected by the Dfs server to the network share containing the Dfs volume files. Established NT share and directory permissions apply.

Connecting to a Dfs Share
Client connections to Dfs shares are performed in the following manner:

The client establishes a connection to the desired Dfs share (for example, \\dragon\dfs\html).
The client checks its local cache for an entry referencing the share.
If the entry is not in cache, the client contacts the Dfs host server.
When the address is resolved, it is added to the local cache.

If a share point has more than one volume, alternates are all presented to the client and stored in cache. The client is supplied with the entire list of alternate volumes when the Dfs connection is made. The client arbitrarily selects which of these alternate volumes to connect to. If the connection between the client and volume fails, the client can select another server from the cached list.

The server that the client considers its Dfs root changes when a client crosses an inter-Dfs junction. The server hosting the new Dfs root now issues its referrals to Dfs shares. When establishing a connection with the new Dfs root, the user credentials that were used to connect to Dfs are passed to the new server. If no credentials were provided to Dfs, the user logon information is used.

Note: Dfs links to NetWare volumes can only be accessed by Windows 95 clients via Microsoft Gateway Services for NetWare (GSNW). If your client has trouble connecting to a NetWare volume via the Dfs share, try connecting directly to the NetWare server with the NetWare path, rather than using the Dfs path. If you can connect this way, check the server hosting the Dfs root to ensure GSNW is running and is correctly configured.

SUMMARY

The new Distributed File System (Dfs) from Microsoft offers administrators a new tool for managing file system resources. In this chapter, I talked about how to use Dfs to unify access to file system resources on your network, and highlighted how Dfs abstracts these distributed resources into a centralized network repository. I walked you through the installation of Dfs onto your NT Server, and explained the configuration of Dfs volumes. Dfs is a powerful network service that enables you to provide your users with transparent access to file system resources distributed throughout your network.

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