Microsoft Distributed File System (Dfs)

1. Microsoft Distributed File System (Dfs) Brett O’Neill CSE 8343 – Group A6

2. Overview • Distributed File Systems • DFS vs. Dfs • What is Dfs? • How Dfs Works • How Users See Dfs • Security • Questions?

3. Distributed File Systems • A distributed file system is a client/server application that allows clients to access data stored on a server as if it were on their own computer. • DFS provides users with a single virtual file store across heterogeneous platforms. • Users are not aware of where files are physically located. • Therefore data can be moved transparently to users.

4. Distributed File Systems (cont.) • When a user accesses a file on the server, the server sends a copy of the file to be cached on the user’s local computer while being processed. Upon completion, the file is sent back to the server. • The DFS organizes file and directory services from various servers into a global directory that can be accessed by any client.

5. Distributed File Systems (cont.) • More than one client can access the same data simultaneously, therefore mechanisms are in place to organize data so the client always receives the most current copy of the data and data conflicts do not arise. • Typically a token system is used to prevent data conflicts. Clients are given tokens with different access rights, usually reads or writes.

6. Distributed File Systems (cont.) • DFS has the capability to replicate files to protect against data access failures. If a server fails, the data can be restored from another server which holds replicated data. • Popular Distributed File Systems: • Sun Microsystems’ NFS • Novell NetWare • IBM/Transarc’s DFS • Microsoft Dfs

7. DFS vs. Dfs • DFS technology was developed years ago as part of the Open Software Foundation’s (OSF) distributed computing environment (DCE) specification. • OSF developed DCE to address interoperability between different UNIX operating systems, and between UNIX and non-UNIX operating systems. • OSF later merged with X/Open to become The Open Group. • Microsoft’s Dfs has nothing to do with DFS, thus the small letters.

8. What is Dfs? • For years, UNIX administrators complained that Microsoft networking lacked a unified directory structure. • To address this shortcoming, Microsoft introduced Dfs to Windows NT 4.0. It is now an integral part of Windows NT 5.0 and Windows 2000.

9. What is Dfs? (cont.) • Dfs is a network server component that unites files on different computers into a single namespace, making it easy to build a single, hierarchical view of multiple file servers and file server shares. • Dfs does for file servers and shares what file systems do for hard disks: file systems provide uniform named access to collections of sectors on disks – Dfs provides uniform naming conventions for collections of servers, shares and files. The result is called a “Dfs tree.”

10. What is Dfs? (cont.) • Example of a Dfs tree:

11. What is Dfs? (cont.) • Without Dfs, system administrators can run out of drive letters because of too many network connections. Consider a network that has file servers for the accounting department, the legal department and the human resources department:

12. What is Dfs? (cont.) • This is obviously quite confusing. Dfs provides a better way to do things. A Dfs administrator can create a single tree structure that includes shares from each department:

13. What is Dfs? (cont.) • Dfs trees make network access easier for users, who no longer have to manually locate which server data is stored on. After connecting to the root of the Dfs tree, users can browse for and access all resources contained within the tree, regardless of where the resources are located. • If a server crashes or must be replaced, or a volume must be moved from one server to another, users do not need to be notified of the change. An administrator simply modifies the Dfs tree to refer to the new server location and users continue to use the same Dfs path to access resources.

14. What is Dfs? (cont.) • Multiple Dfs trees can exist on a network. There can be different trees for each type of user. For example, a different tree can be created for the legal, human resources and accounting departments. • Any volume can be included in one or more Dfs trees.

15. How Dfs Works • Dfs organizes shared-file resources into a tree structure. A shared-file resource can be accessed by either its Dfs path name or its \\servername\sharename path. • Each Dfs tree has one root volume. The root volume can have leaf volumes beneath it. Leaf volumes can be physically located on different servers than the root volume.

16. How Dfs Works (cont.) • The root volume must be hosted on a Windows NT or Windows 2000 server running Dfs. • Leaf volumes can be hosted on any type of Microsoft server or any server with Windows NT-based client server software. • Banyan volumes cannot be added to Dfs trees.

17. How Dfs Works (cont.) • Each volume can contain multiple levels of folders. • Dfs trees can be nested inside other Dfs trees to create multi-leveled trees. This is done by adding the root volume of one Dfs tree as a leaf volume in another Dfs tree. • Multi-level trees are transparent to users. They are unaware when they have crossed from one Dfs tree to another.

18. How Dfs Works (cont.) • Some volumes in a tree can use one or more shared folders for storage. For example: \\human_resources\dfs\benefits \\benefits\information \\benefits2\information • In this case, the volume has alternate paths. • Alternate paths provide load-balancing and allow data to be accessed if one server crashes.

19. How Dfs Works (cont.) • A root volume can span multiple servers, eliminating single point of failure problems. • Shared resources can be replicated using Windows File Replication Service (FRS) to increase their availability. • Replication of large amounts of data can be scheduled at off-hours to prevent congesting a local LAN or slow WAN links.

20. How Users See Dfs Trees • Dfs resources are viewed and accessed just like any other resources on a network. To users, the Dfs root volume appears just like a share name of a shared folder. • Users can browse through a tree transparently, regardless of 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 root folder of a Dfs tree.

21. How Users See Dfs Trees • When a user views the contents of a root volume, they see the leaf volumes located under the root and the contents of the shared folder that comprises the root. • Users of Windows NT 4.0 and greater, Windows 2000, or Windows 95 with Dfs client software can see and access Dfs trees. Users of older Microsoft operating systems can still use conventional \\servername\sharename syntax to access shared folders that are part of Dfs trees.

22. Security • Dfs does not add any permissions or security limitations beyond those already assigned to files or shares themselves. • A user can access a volume in the Dfs tree if the user has permission to access the shared folder directly. • Users do not need permission to access the root volume in order to access leaf volumes. • Only administrators can administer a Dfs tree.

23. Questions?