dfsdoc.htm

# Microsoft Distributed File System for Microsoft Windows NT Server 4.0 Administrator's Guide

## Contents

Practical Uses of Dfs Trees
How Dfs Works
How Users See and Connect To Dfs Trees
Administering Dfs Trees

Microsoft® Distributed File System for Microsoft Windows NT® Server (Dfs) enables distributed file system capabilities on Windows NT Server. A distributed file system provides a single tree structure for multiple shared volumes located on different servers on a network. A user accessing a volume on a Dfs tree does not need to know the name of the server where the volume is actually shared.

With the Dfs software, you can create a Dfs tree root on any server running the Windows NT Server software released at the PDC. Windows NT Server version 4.0.

This document explains what Dfs is, why it is useful, and how to create and administer Dfs trees.

# Practical Uses of Dfs Trees

A Dfs tree makes network access easier for users, who no longer have to manually locate which server any particular resource is on. After connecting to the root of the Dfs tree, they can then browse for and access all resources contained within the tree, no matter which server on which the resource is physically located.

With Dfs, if a server goes down and you need to replace it, or you need to move a volume from one server to another, you can do so without informing users of the change. Instead, you modify the Dfs tree to refer to the new server location for the resource, and users can continue to use the same Dfs path to access the volume.

Because you can have multiple Dfs trees on your network, you can create a different Dfs tree for each type of user on your network. For example, an engineering firm could create one Dfs tree containing all the volumes needed by their engineers, another for payroll and benefits people, and so on. Any particular volume can be included in one or more Dfs trees, ensuring that every user can access all the resources they need.

With Dfs, you can increase data availability and transparently distribute load across multiple servers. This is because multiple servers can serve as duplicate storage points for a single volume.

Dfs gives you the flexibility to expand your network as smoothly as possible. When you add disk storage to your network, the physical server on which you add it can be independent of where in the logical namespace the new storage is made available.

Dfs also complements Microsoft Internet Information Server. For example, if you set up a World Wide Web site on your network, you could have the root of the web site be the root of a Dfs tree. If you later move a resource within the Dfs tree, all HTML links will continue to work.

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# How Dfs Works

Dfs organizes your shared-file resources into a tree structure. A shared-file resource that is part of a Dfs tree can be accessed by either its Dfs path name or its \\servername\sharename path.

Each Dfs tree has one or more root volumes. In this release, you can have one level of volumes, called leaf volumes, beneath the root level. Leaf volumes can be physically located on different servers than the root volume. (Future releases of Dfs will include support for multiple levels of volumes under a root).

A Dfs tree that has more than one root volume is called a fault tolerant dfs tree. The contents of the multiple root volumes are identical, and provide multiple points of failure for the entire tree. A Dfs tree that is configured to always have only one root volume is called a standalone Dfs tree.

The root volumes of Dfs trees must be hosted on a server running the PDC release of Windows NT Server.

Figure 1 shows a sample standalone Dfs tree. The Dfs paths to each volume are shown in bold, while the network paths are shown in italics.

Figure 1-- A sample Dfs tree structure

You can have multiple Dfs trees on your network. Any shared folder can be a volume in multiple Dfs trees.

The various folders on a particular server can be made volumes on different Dfs trees, but a server can have only one folder that serves as a Dfs root.

Dfs automatically creates short file and directory names for long names, so that 16-bit applications can use Dfs paths to access files.

## Nesting and Expanding Dfs Trees

Although each particular Dfs tree in this release is limited to two levels of volumes, each volume can contain multiple levels of folders. Additionally, you can create a multileveled tree by nesting Dfs trees inside of each other. You do this by adding the root volume of one Dfs tree as a leaf volume in another Dfs. Creating a multilevel tree this way is transparent to users; they do not know when they have crossed from one Dfs tree to another.

You can also add levels to a Dfs tree by using the local storage of the server hosting the root volume. Any files and folders under the Dfs root volume will be visible through the Dfs tree. In addition, when you add leaf volumes to a Dfs tree, you can add them under folders at any level under the Dfs volume directory. In the sample in Figure 1, info is a folder added locally at the server under the folder shared as dfs. The reports and releases volumes are added under the info folder.

## Volumes That Include Alternate Paths

Note that some volumes on a Dfs tree (such as \\human_resources\dfs\benefits in the example in Figure 1) can use one or more shared folders for storage. If a volume uses more than one shared folder, it has alternate paths.

Alternate paths provide load balancing, and allow the volume to be accessed even if one of the volume servers goes down. However, the Dfs software does not replicate information between the two servers; network administrators must ensure that the data on the servers stays synchronized through other means.

Because the Dfs software does not synchronize alternate paths automatically (without third-party replication software), alternate paths are best suited for read-only volumes, where users will not be adding files or modifying existing files.

## Security

The Dfs software does not add any permissions or security limitations beyond those already assigned to the files or shares themselves. A user can access a volume through the Dfs tree as long as the user has permission to access the shared folder directly.

It is not necessary for a user to have permissions for a root volume in order to access leaf volumes. For example, in the tree in Figure 1, if a user has permissions for the share \\insurance\public (located in the Dfs as \\human_resources\dfs\insurance), then the user can access that share through the Dfs tree, even if the user does not have permissions for the \\human_resources\dfs share.

Only administrators can administer a Dfs tree.

## Local File Structure on Servers that Contain Root Volumes

When you add a leaf volume to a Dfs tree, a blank folder is automatically created in the root volume directory. This blank folder serves as a junction point to the leaf volume.

Dfs prevents you from deleting any of these folders manually. If you use Dfs Administrator to remove a volume, the junction point folder is automatically removed.

If you delete the Dfs software from a root server without first removing the leaf volumes from the Dfs tree it hosted, you can then delete the junction point folders manually.

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# How Users See and Connect To Dfs Trees

Users view and access resources through a Dfs tree just as they view and access other resources on the network. When browsing a network, a Dfs root appears just like a share name of a shared folder. Fault-tolerant Dfs trees appear as \\domain_name\dfsname, while standalone Dfs trees appear as \\servername\dfsname. For example, with the sample Dfs tree in Figure 1, a user browsing the network would see dfs as a shared directory available under the human_resources server.

Users can browse through a tree transparently, no matter the location of each volume or the file system used for that volume. Users can make connections to and assign local drive letters to the any folder of a Dfs tree.

When a user views the contents of the root volume through its Dfs name, they see both the Dfs volumes located under that volume, as well as any contents of the shared folder that comprises the root volume. For example, in Figure 1, when a user views the contents of \\human_resources\dfs, they see the benefits, insurance, and health Dfs volumes, as well as any files and folders located in the \\human_resources\dfs folder.

Users of computers with the PDC Windows NT software can see and access Dfs trees.

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# Administering Dfs Trees

You administer Dfs trees by using the Dfsadmin tool.

With Dfsadmin, you can add and remove volumes to a Dfs tree, modify volumes, create alternate paths to a volume, and view and configure information about the volumes contained in a tree. You can remotely administer any Dfs tree on the network that you have permissions for.

#### To start Dfsadmin

1. On the Start menu, click Programs, then click Administrative Tools, then click Dfs Administrator.
   -Or-
   On the Start, menu, click Run. In the Open box, type dfsadmin, and then click OK.

If the local server already hosts a Dfs tree, you can begin administering it. Otherwise, you can either create a Dfs tree on the local server, or remotely administer another Dfs tree. To remotely administer a Dfs tree, click No when prompted whether to host a Dfs, then select the tree to administer.

If you want to create a Dfs root on the local computer, see the following section, "Creating a New Dfs Tree Root."

## Creating a New Dfs Tree Root

To create a Dfs tree root in this release, you must work physically at the server on which you want to create the root.

#### To create a root volume for a new Dfs tree

1. While working physically at the server which will host the root, start Dfsadmin. (To do so, on the Start menu, click Programs, then click Administrative Tools, then click Dfs Administrator.)
2. Click Yes to create a Dfs root (host).
3. Click either Create a new Fault Tolerant Dfs in this domain or Create a Stand Alone Dfs on this machine, then click OK.
4. Under Host a Dfs on share, select the shared directory that will serve as the root. Or, to use a new share as the root, click New Share and specify the folder. Then click OK.
5. Click Yes to restart the computer.

If you click No when prompted whether to host a Dfs, you can choose an existing Dfs tree to remotely administer. If, during this time, you then decide to start hosting a Dfs tree on the local computer, use the following procedure:

#### To create a root volume for a new Dfs tree after starting Dfsadmin

1. On the Dfs menu, click Configure Dfs.
2. Click either Create a new Fault Tolerant Dfs in this domain or Create a Stand Alone Dfs on this machine, then click OK.
3. Under Host a Dfs on share, select the shared directory that will serve as the root. Or, to use a new share as the root, click New Share and specify the folder. Then click OK.
4. Click Yes to restart the computer.

## Creating Another Root-Level Participant Volume

Fault-tolerant Dfs trees can have multiple servers which all host identical copies of a root volume of a Dfs tree. This provides multiple point of failure for the entire tree.

To configure this, first create the original root volume by following the procedure in "Creating a New Dfs Tree Root" (and be sure to select Create a new Fault Tolerant Dfs in this domain). Then create the other root-level participants by using the following procedure.

To create another root-level participant

1. While working physically at the server which will host the root, start Dfsadmin.
2. Click Yes to create a Dfs root (host).
3. Click Join an Existing Fault Tolerant Dfs in this domain, then click OK.
4. Under Host a Dfs on share, select the shared directory that will serve as the Dfs volume. Or, to use a new share as the Dfs volume, click New Share and specify the folder. Then click OK.
5. Click Yes to restart the computer.

## Stop Hosting a Dfs Root Volume

Use this procedure to stop hosting a Dfs root on a server.

To stop hosting a Dfs root volume

1. While working physically at the server, start Dfsadmin.
2. In the Dfs menu, click Stop Hosting Dfs.

## Adding a Leaf Volume to a Dfs Tree

Any folder you want to add to a Dfs tree must already be shared.

#### To add a volume to a Dfs tree

1. In the Dfsadmin main window, select the volume under which you want the new volume to appear.
2. On the Dfs menu, click Add To Dfs.
3. Under When a user references this path, type the volume name for the new volume as an extension of a current volume in the tree. For example, if you are creating the \\human_resources\dfs\insurance volume in Figure 1, you would type insurance immediately after \\human_reosources\dfs\. (To add the new volume farther down in the directory tree, type as much of the path as you need; for example, to create the \\human_resources\dfs\info\reports volume, you would type info\reports after \\human_resources\dfs\.) You can use the Browse button to browse the current structure of the Dfs tree, and select the Dfs path to append your new volume to.
4. Under Send the user to this network path, type the path of the shared folder to add as a volume. (Or use the Browse button to browse the network and select the volume.)
5. Optionally, type a comment in the Comment box.
6. Click OK.

## Removing a Leaf Volume from a Dfs Tree

#### To remove a volume from the Dfs

1. In the Dfsadmin main window, select the volume to remove.
2. On the Dfs menu, click Remove From Dfs.
3. Click Yes.

## Adding Alternate Paths for a Volume

A volume can use one or more shared folders for its storage. If the volume uses more than one, it has alternate paths.

When a volume includes alternate paths, user requests to access the volume are distributed among the alternate paths.

The Dfs software does not ensure that the contents of the alternate paths of a volume are replicated. Network administrators must manually ensure that the alternates stay synchronized.

#### To add an alternate path for a volume

1. In the Dfsadmin main window, double-click the volume.
2. Click Add.
3. Click Yes.
4. Under Send the user to this network path, type the path of the shared folder to add as an alternate path for the volume.

## Removing a Volume's Alternate Path

#### To remove an alternate path from a volume

1. In the Dfsadmin main window, double-click the volume.
2. Under Send the user to this network path, select the network path you want to remove.
3. Click Remove.
4. Click OK.

## Saving and Restoring the Dfs Structure Table

You can save the current structure of the Dfs tree to a file, which you can later reload to restore the Dfs volume structure. Note that this saves only the links between volumes, not any volume contents. The save files are server-specific comma separate files, with a .csv file extension

#### To save the current Dfs tree structure

1. On the Dfs menu, click Save As.
2. Type a name for the file in the File name box, and then click Save.

#### To restore a previous Dfs tree structure

1. On the Dfs menu, click Load.
2. Select the file to restore, and then click Open.

## Filtering the View of Volumes

You can filter the list of volumes shown in the Dfsadmin main window. You can filter volumes by name, comment, and the number of alternate servers that provide storage for the volume.

#### To filter the list of volumes

1. On the View menu, click Filter.
2. Click the filtering option you want, and then click OK.

For more information on any of the filtering options, right-click the option and then click What's This?

## Stopping and Starting the Dfs Service

Dfs is implemented as a service (the Distributed File Service).

You can start and stop the service manually by using either Services in Control Panel or the command line. The commands are net stop dfs and net start dfs.

## Administering a DFS Tree From the Command Prompt

DFS provides the following commands you can use from the command prompt.

dfscmd /map \\dfsname\dfsshare\path \\server\share\path [comment]
  Adds the shared folder \\server\share\path as a volume in the specified Dfs tree.
dfscmd /unmap \\dfsname\dfsshare\path
  Removes the volume from the Dfs tree.
dfscmd /add \\dfsname\dfsshare\path \\server\share\path
  Adds \\server\share\path as an alternate path for the specified Dfs volume.
dfscmd /remove \\dfsname\dfsshare\path \\server\share\path
  Removes the specified alternate path from the specified volume.
dfscmd /view \\dfsname\dfsshare [/partial | /full]
  Displays all the volumes in the Dfs tree. Without arguments, only the volume names are displayed. Specifying /partial causes comments for each volume to also be displayed. Specifying /full causes the network path of each volume (including all alternate paths) to be displayed.

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