Microsoft Distributed File System Dfs Brett O Neill CSE 8343 Group A6 1 Overview Distributed File Systems DFS vs Dfs What is Dfs How Dfs Works How Users See Dfs Security Questions 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 What is Dfs cont Example of a Dfs tree 10 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 11 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 12 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 13 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 14 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 15 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 16 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 17 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 18 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 19 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 20 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