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Microsoft Microsoft Distributed File Distributed File

System (Dfs)System (Dfs)Brett O’NeillBrett O’Neill

CSE 8343 – Group A6CSE 8343 – Group A6

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OverviewOverview Distributed File SystemsDistributed File Systems DFS vs. DfsDFS vs. Dfs What is Dfs?What is Dfs? How Dfs WorksHow Dfs Works How Users See DfsHow Users See Dfs SecuritySecurity Questions?Questions?

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Distributed File SystemsDistributed File Systems A distributed file system is a A distributed file system is a

client/server application that client/server application that allows clients to access data allows clients to access data stored on a server as if it stored on a server as if it were on their own were on their own computer.computer.

DFS provides users with a DFS provides users with a single virtual file store single virtual file store across heterogeneous across heterogeneous platforms.platforms.

Users are not aware of Users are not aware of where files are physically where files are physically located.located.

Therefore data can be Therefore data can be moved transparently to moved transparently to users.users.

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Distributed File Systems Distributed File Systems (cont.)(cont.)

When a user accesses a file on the server, When a user accesses a file on the server, the server sends a copy of the file to be the server sends a copy of the file to be cached on the user’s local computer cached on the user’s local computer while being processed. Upon completion, while being processed. Upon completion, the file is sent back to the server.the file is sent back to the server.

The DFS organizes file and directory The DFS organizes file and directory services from various servers into a services from various servers into a global directory that can be accessed by global directory that can be accessed by any client.any client.

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Distributed File Systems Distributed File Systems (cont.)(cont.)

More than one client can access the same More than one client can access the same data simultaneously, therefore data simultaneously, therefore mechanisms are in place to organize data mechanisms are in place to organize data so the client always receives the most so the client always receives the most current copy of the data and data current copy of the data and data conflicts do not arise.conflicts do not arise.

Typically a token system is used to Typically a token system is used to prevent data conflicts. Clients are given prevent data conflicts. Clients are given tokens with different access rights, tokens with different access rights, usually reads or writes.usually reads or writes.

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Distributed File Systems Distributed File Systems (cont.)(cont.)

DFS has the capability to replicate DFS has the capability to replicate files to protect against data access files to protect against data access failures. If a server fails, the data can failures. If a server fails, the data can be restored from another server which be restored from another server which holds replicated data.holds replicated data.

Popular Distributed File Systems:Popular Distributed File Systems: Sun Microsystems’ NFSSun Microsystems’ NFS Novell NetWareNovell NetWare IBM/Transarc’s DFSIBM/Transarc’s DFS Microsoft DfsMicrosoft Dfs

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DFS vs. DfsDFS vs. Dfs DFS technology was developed years ago as DFS technology was developed years ago as

part of the Open Software Foundation’s (OSF) part of the Open Software Foundation’s (OSF) distributed computing environment (DCE) distributed computing environment (DCE) specification.specification.

OSF developed DCE to address OSF developed DCE to address interoperability between different UNIX interoperability between different UNIX operating systems, and between UNIX and operating systems, and between UNIX and non-UNIX operating systems.non-UNIX operating systems.

OSF later merged with X/Open to become The OSF later merged with X/Open to become The Open Group.Open Group.

Microsoft’s Dfs has nothing to do with DFS, Microsoft’s Dfs has nothing to do with DFS, thus the small letters.thus the small letters.

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What is Dfs?What is Dfs? For years, UNIX administrators For years, UNIX administrators

complained that Microsoft complained that Microsoft networking lacked a unified directory networking lacked a unified directory structure.structure.

To address this shortcoming, To address this shortcoming, Microsoft introduced Dfs to Windows Microsoft introduced Dfs to Windows NT 4.0. It is now an integral part of NT 4.0. It is now an integral part of Windows NT 5.0 and Windows 2000.Windows NT 5.0 and Windows 2000.

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What is Dfs? (cont.)What is Dfs? (cont.) Dfs is a network server component that unites Dfs is a network server component that unites

files on different computers into a single files on different computers into a single namespace, making it easy to build a single, namespace, making it easy to build a single, hierarchical view of multiple file servers and hierarchical view of multiple file servers and file server shares.file server shares.

Dfs does for file servers and shares what file Dfs does for file servers and shares what file systems do for hard disks: file systems provide systems do for hard disks: file systems provide uniform named access to collections of sectors uniform named access to collections of sectors on disks – Dfs provides uniform naming on disks – Dfs provides uniform naming conventions for collections of servers, shares conventions for collections of servers, shares and files. The result is called a “Dfs tree.”and files. The result is called a “Dfs tree.”

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What is Dfs? (cont.)What is Dfs? (cont.) Example of a Dfs Example of a Dfs

tree:tree:

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What is Dfs? (cont.)What is Dfs? (cont.) Without Dfs, system Without Dfs, system

administrators can administrators can run out of drive run out of drive letters because of too letters because of too many network many network connections. connections. Consider a network Consider a network that has file servers that has file servers for the accounting for the accounting department, the legal department, the legal department and the department and the human resources human resources department:department:

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What is Dfs? (cont.)What is Dfs? (cont.) This is obviously This is obviously

quite confusing. Dfs quite confusing. Dfs provides a better provides a better way to do things. A way to do things. A Dfs administrator Dfs administrator can create a single can create a single tree structure that tree structure that includes shares includes shares from each from each department: department:

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What is Dfs? (cont.)What is Dfs? (cont.) Dfs trees make network access easier for Dfs trees make network access easier for

users, who no longer have to manually locate users, who no longer have to manually locate which server data is stored on. After which server data is stored on. After connecting to the root of the Dfs tree, users connecting to the root of the Dfs tree, users can browse for and access all resources can browse for and access all resources contained within the tree, regardless of where contained within the tree, regardless of where the resources are located.the resources are located.

If a server crashes or must be replaced, or a If a server crashes or must be replaced, or a volume must be moved from one server to volume must be moved from one server to another, users do not need to be notified of the another, users do not need to be notified of the change. An administrator simply modifies the change. An administrator simply modifies the Dfs tree to refer to the new server location Dfs tree to refer to the new server location and users continue to use the same Dfs path to and users continue to use the same Dfs path to access resources.access resources.

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What is Dfs? (cont.)What is Dfs? (cont.) Multiple Dfs trees can exist on a Multiple Dfs trees can exist on a

network. There can be different trees network. There can be different trees for each type of user. For example, a for each type of user. For example, a different tree can be created for the different tree can be created for the legal, human resources and legal, human resources and accounting departments.accounting departments.

Any volume can be included in one or Any volume can be included in one or more Dfs trees.more Dfs trees.

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How Dfs WorksHow Dfs Works Dfs organizes shared-file resources into a Dfs organizes shared-file resources into a

tree structure. A shared-file resource can tree structure. A shared-file resource can be accessed by either its Dfs path name be accessed by either its Dfs path name or its or its \\servername\sharename\\servername\sharename path. path.

Each Dfs tree has one Each Dfs tree has one root volumeroot volume. The . The root volume can have root volume can have leaf volumesleaf volumes beneath it. Leaf volumes can be beneath it. Leaf volumes can be physically located on different servers physically located on different servers than the root volume.than the root volume.

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How Dfs Works (cont.)How Dfs Works (cont.) The root volume must be hosted on a The root volume must be hosted on a

Windows NT or Windows 2000 server Windows NT or Windows 2000 server running Dfs.running Dfs.

Leaf volumes can be hosted on any Leaf volumes can be hosted on any type of Microsoft server or any server type of Microsoft server or any server with Windows NT-based client server with Windows NT-based client server software.software.

Banyan volumes cannot be added to Banyan volumes cannot be added to Dfs trees.Dfs trees.

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How Dfs Works (cont.)How Dfs Works (cont.) Each volume can contain multiple levels Each volume can contain multiple levels

of folders. of folders. Dfs trees can be nested inside other Dfs Dfs trees can be nested inside other Dfs

trees to create multi-leveled trees. This is trees to create multi-leveled trees. This is done by adding the root volume of one done by adding the root volume of one Dfs tree as a leaf volume in another Dfs Dfs tree as a leaf volume in another Dfs tree.tree.

Multi-level trees are transparent to Multi-level trees are transparent to users. They are unaware when they have users. They are unaware when they have crossed from one Dfs tree to another.crossed from one Dfs tree to another.

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How Dfs Works (cont.)How Dfs Works (cont.) Some volumes in a tree can use one or more Some volumes in a tree can use one or more

shared folders for storage. For example:shared folders for storage. For example:\\human_resources\dfs\benefits\\human_resources\dfs\benefits

\\benefits\information\\benefits\information\\benefits2\information\\benefits2\information

In this case, the volume has alternate paths.In this case, the volume has alternate paths. Alternate paths provide load-balancing and Alternate paths provide load-balancing and

allow data to be accessed if one server allow data to be accessed if one server crashes.crashes.

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How Dfs Works (cont.)How Dfs Works (cont.) A root volume can span multiple servers, A root volume can span multiple servers,

eliminating single point of failure eliminating single point of failure problems.problems.

Shared resources can be replicated using Shared resources can be replicated using Windows File Replication Service (FRS) to Windows File Replication Service (FRS) to increase their availability.increase their availability.

Replication of large amounts of data can Replication of large amounts of data can be scheduled at off-hours to prevent be scheduled at off-hours to prevent congesting a local LAN or slow WAN links.congesting a local LAN or slow WAN links.

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How Users See Dfs TreesHow Users See Dfs Trees Dfs resources are viewed and accessed Dfs resources are viewed and accessed

just like any other resources on a network. just like any other resources on a network. To users, the Dfs root volume appears just To users, the Dfs root volume appears just like a share name of a shared folder.like a share name of a shared folder.

Users can browse through a tree Users can browse through a tree transparently, regardless of the location of transparently, regardless of the location of each volume or the file system used for each volume or the file system used for that volume.that volume.

Users can make connections to and assign Users can make connections to and assign local drive letters to the root folder of a local drive letters to the root folder of a Dfs tree.Dfs tree.

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How Users See Dfs TreesHow Users See Dfs Trees When a user views the contents of a root When a user views the contents of a root

volume, they see the leaf volumes located volume, they see the leaf volumes located under the root and the contents of the shared under the root and the contents of the shared folder that comprises the root.folder that comprises the root.

Users of Windows NT 4.0 and greater, Users of Windows NT 4.0 and greater, Windows 2000, or Windows 95 with Dfs client Windows 2000, or Windows 95 with Dfs client software can see and access Dfs trees. Users software can see and access Dfs trees. Users of older Microsoft operating systems can still of older Microsoft operating systems can still use conventional use conventional \\servername\sharename\\servername\sharename syntax to access shared folders that are part syntax to access shared folders that are part of Dfs trees.of Dfs trees.

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SecuritySecurity Dfs does not add any permissions or Dfs does not add any permissions or

security limitations beyond those already security limitations beyond those already assigned to files or shares themselves.assigned to files or shares themselves.

A user can access a volume in the Dfs tree A user can access a volume in the Dfs tree if the user has permission to access the if the user has permission to access the shared folder directly.shared folder directly.

Users do not need permission to access the Users do not need permission to access the root volume in order to access leaf root volume in order to access leaf volumes. volumes.

Only administrators can administer a Dfs Only administrators can administer a Dfs tree.tree.

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Questions?Questions?