Step-by-Step Guide to Distributed File System (Dfs)
Because shared files are widely distributed across networks, administrators face growing problems as they try to keep users connected to the data they need. The distributed file system (Dfs) provides a mechanism for administrators to create logical views of directories and files, regardless of where those files physically reside in the network. Fault tolerance of network storage resources is also possible using Dfs. This guide describes how to use the Dfs Share Creation wizard.
The examples provided in this document assume you have already configured the Active Directory® service, and have administrator permissions for both the domain and the server where you will be configuring Dfs.
Using the Dfs Administrator Tool
This step-by-step guide describes how to use the Dfs Administrator snap-in. Installation of the Dfs service takes place automatically during Windows 2000 Server Setup. However, you must configure Dfs in order for a Dfs share to be accessible to clients.
Perform these steps on the domain controller while logged on as a user with administrative privileges.
In the Windows 2000 operating system, Dfs can integrate with Active Directory to create fault tolerant Dfs roots on Windows 2000 domain controllers (DCs) and member servers. If you have multiple servers in your Windows 2000 domain, any or all participating servers can host and provide fault tolerance for a given Dfs root. Active Directory is used to ensure domain controllers in the domain share a common Dfs topology, thus providing redundancy and fault tolerance.
Alternatively, you can create a stand-alone Dfs server, which does not take advantage of Active Directory and does not provide root level fault tolerance. A DC can host a single Dfs root, and you can have an unlimited number of Dfs roots in each domain. Up to 32 DCs can host the same root. Multiple Dfs root volumes can be hosted in the domain. Additional computers hosting the root or child nodes (links) improves load balancing, fault tolerance, and site preference to directory service-aware network clients. Dfs links below the root can reside on any UNC path accessible to the Dfs server and clients.
In this guide, it is assumed you are creating a fault-tolerant Dfs Root.
If you have multiple domain controllers hosting a fault tolerant Dfs root, keep in mind that fault tolerant Dfs uses Active Directory to store topology knowledge. Thus, it is necessary for the topology knowledge to converge between the domain controllers. Updates to the Dfs configuration initially take place on the host server in the Windows 2000 domain. Domain controllers may have a different view of the Dfs configuration until multimaster replication from the Dfs host makes changes fully replicated between all domain controllers in a domain. Dfs—the root and all its links—is stored as a single entity known as a blob. When a change is made to the blob, the whole blob replicates until consistent throughout the domain.
This takes about five minutes between any given two replicating domain controllers in the same site, and at least 15 minutes if the domain controllers are in different sites. Until convergence occurs, Dfs administrator tools located on different Dfs clients can be presented with a different Dfs configuration. You can click Refresh to update Dfs with the current configuration from the Dfs host.
At this point, you have an empty Dfs root in Active Directory. For this share to be interesting to users, you need to publish non-local shares in the Dfs namespace.
To publish non-local shares
Note: For replication to be enabled, the shares for the Dfs root or link must reside on an NTFS 5.0 formatted partition on a Windows 2000 domain controller or member server. The Primary flag marks the specified servers' files and folders as authoritative the first time replication takes place, after which normal multimaster replication takes place.
The DFS root snap-in now looks like the one illustrated below.
Test Drive the Dfs
Any user of Windows 2000 logged on to your domain can now access the fault tolerant Dfs. Assuming they have proper access privileges, they can negotiate the individual junctions by using the following commands.
In the example used in the document, the command would be:
In a production environment, this alternate drive could reside on another server or on a user’s workstation. Any user accessing the fault tolerant share would be able to continue to work uninterrupted. Scheduled file server maintenance, software upgrades, and other tasks that normally require taking a server off-line can now be accomplished without user disruption.
To access the Dfs root using Windows Explorer
You can also turn off one of the two servers and access the same Dfs path. This will show the failover that occurs when a server in the Dfs namespace becomes unavailable. Note that this takes place for fault tolerant roots and child nodes that are backed by more than one server.
Note: Regarding Microsoft Cluster service, at present, Dfs supports Microsoft Cluster service using machine-based Dfs only. You cannot create fault tolerant Dfs topologies on systems running Microsoft Cluster service.
If you are using fault tolerant Dfs where multiple domain controllers exist, it is important to consider that the Dfs configuration requires time to converge between domain controllers in the domain. For immediate replication, install and use the REPLMon tool that is found in the support\tools directory of the Windows 2000 Server product CD-ROM.
Dfs-aware clients using earlier versions of the operating system (such as Windows NT 4.0) are not able to connect with fault tolerant Dfs roots. They can, however, connect directly to individual Dfs roots that participate in a fault tolerant Dfs. To do this, substitute the machine name for the domain name in the above Net Use command.
Windows NT-based workstations browsing Dfs can also verify what physical storage they are referencing by viewing the Dfs tab available in System Properties found in Windows Explorer.
Note: Most administrative functions can be performed from the command line or scripted using DFSCMD.EXE. Type DFSCMD /? for online help.
You can later modify the properties of this object.
You can also publish your fault tolerant Dfs root as a shared folder in the directory service, and then access it using any directory service browsing tools. From the Active Directory Management snap-in, select your domain, right-click New, Volume. Fill in the appropriate information.