DFS Replication in Win 2k3 Server R2

In present day set up, users in branch offices in an enterprise need access

to shared folders and files stored in another branch or a data center located at

some other geographic location. This process has been made simpler in Windows

2003 Server R2 with the introduction of various new technologies; one of them is

DFS Replication, which we will talk about in this article.

DFS Replication is the successor of DFS Windows 2000 Server's FRS (File

Replication Service). In Windows 2003 R2, DFS Replication is an engine that does

replication scheduling and bandwidth throttling. It uses RDC (Remote

Differential Compression) algorithm. RDC is a client-server protocol that

updates files over a limited-bandwidth network and can detect insertions,

re-arrangements of data in files and in turn enables DFS Replication to

replicate only the changed file blocks when the files are updated.

Associated technologies



Another feature called Cross-file RDC, contained in the same R2 pack, reduces
the amount of bandwidth required to replicate new files. There is also an

enhanced feature with it called as the DFS Namespaces. It was earlier introduced

in Windows 2003 Server SP1 as Distributed File System technology. It allows

administrators to group shared folders located on different servers and present

them to users as a virtual tree of folders known as a namespace. In its new

enhancements, it has processes like Client Failover in which clients can access

another server, after one of the servers has failed in the namespace. Another

process is Target Priority in which a client accesses a namespace; the client

receives a referral that contains a list of targets associated with the

namespace root or folder. To fine-tune how particular targets are ordered,

administrators can specify whether a server appears first or last in a referral.

DFS Namespaces and DFS Replication together are used to publish documents,

software, and data to users in an enterprise. Even though DFS Replication alone

can be used for distributing data, using DFS Namespaces allows administrators to

configure the namespace so that a folder in the namespace can be hosted by

multiple servers. When users browse namespace, they see a single folder and are

not aware that the folder is hosted by multiple servers. When a change occurs on

one folder, they are replicated to all members of the replication group. The RDC

component detects changes on the volume by continuously monitoring the update

sequence number (USN) journal, and DFS Replication replicates changes only after

the file is closed. Also in DFS Replication when a file is changed, only the

changed blocks are replicated, not the entire file and RDC protocol determines

the altered file blocks and transfers only the changed fraction of the file over

the network. Each DFS server can support a maximum of 256 replication groups and

each of these groups can contain up to 256 replicated folders. You can configure

one or more sets of folders and servers as a replication group with a common

configuration for replicated folders, replication schedule, and bandwidth

throttling.

In R2 you can create DFS health report anytime to find out status of replication servers as well as details of errors and warnings given by the servers

Using DFS snap-in present in R2, administrators can easily add new servers

and pre-stage the replicated folders on the target servers by copying the data

to the servers or restoring a backup etc. If the files on the target server are

out-of-date, DFS Replication will use RDC to replicate only the changes that

occurred since the data was pre-staged. If any pre-staged files or folders exist

on the target servers, which are not present on the source server, they are

moved to the 'PreExisting' folder under the target server's replicated folder

path. In DFS Replication all global configurations are stored in Active

Directory (AD) and are also cached in a local .xml file on each member. If a

member crashes or the file becomes corrupted, DFS Replication can easily rebuild

the file using the settings stored in AD.

Implement DFS Replication



First thing you need to do is to install DFS Management Component and DFS
Replication Service. For this install Open DFS Management from the

Administrative tools to open DFS Management console. To create a new namespace,

right-click on the Namespaces option and select New Namespace. A wizard will

start; first it will ask you to provide the Name of Server, where namespace will

be hosted, and then you need to give a name to Namespace you are creating, let's

say 'dfstest'. Now it will ask whether you want your Namespace to be domain

based or standalone; here choose Domain and go to create Namespace, confirm the

settings and close the wizard. Now expand the namespaces and select just created

namespace i.e. dfstest and go to Namespace Servers tab. Here from the Actions

panel, click Add Namespace Server. In Namespace server field, provide the name

of another server to host the namespace and click 'Yes' when asked to start the

DFS service.

Now to create a folder in namespace with target in DFS Management console,

click New Folder and provide it a name. Next go to this just created folder

again and click New Folder. Provide it a name lets say 'test' and select Add to

add a folder target. Click Browse to browse for Shared Folders and in next step

provide the name of the server that will host this 'test' shared folder. Now, to

enable DFS Replication on the 'test' folder, from the DFS management console,

right-click on the 'test' folder, and then click Replicate Folder. This will

start the Replicate Folder Wizard, here it will first ask you to provide a name

for Replication Group, Replicated Folder Name and Replication Eligibility.

Select defaults. Next, in primary member window, choose any member, if the

folder targets are empty. And if both folder targets contain content, choose the

member that has the most up-to-date content. In the Topology Selection window

Select Full Mesh and in Replication Group Schedule and Bandwidth option choose

Replicate continuously using the specified bandwidth. Lastly click on Create the

Replication group and finish the wizard. A new replication group should now

appear in Replication option in the console tree. Now if you want you can try

browsing the namespace to see if it's working properly.