Directory Services/Active Directory

Ulf B. Simon-Weidner's Blog
Windows Server 2003 R2: DFS out of the Branch Office Solutions
Here's another component of Windows Server 2003 R2 - specifically the Branch Office Solutions - I'm looking forward too: The new Release of the Distributed File System (DFS).
 
DFS is available since Windows NT 4.0 and provides the possibility to "hide all many shares behind a single share": You can build up a DFS-Root (the share the users connect to) and put Folders (DFS-Links) underneath it. Those look for the user as regular folders, but in reality they point to different shares on different servers.
Since Windows 2000 there are two different options when creating a DFS-Root: a domain DFS Root or a standalone Root. The Domain DFS-Root is integrated into Active Directory, users connect to \\domain.com\myDfsRoot, the standalone DFS-Root is on a single server or on a clustered server and users connect to \\servername.domain.com\myDfsRoot.
 
In Windows 2000 you also had the possibility to link multiple servers to a DFS-Link (Folder), and you usually were configuring replication between those shares. The big advantage is that users are connecting to the folder which is in their own site, but are able to fail over to another site if the local server is not online. For the replication of the content FRS (File Replication Services) is used, the same replication engine which takes care of replicating Sysvol (the share which the clients use to retrieve their logon-Scripts and Policies when logging on).
 
With Windows Server 2003 R2 DFS is split into two parts: DFS-Namespace (formerly known as DFS) and DFS-Replication (formerly provided by FRS). Those provide the following advantages (thanks to ~eric for correcting my prior statement about RDC):
  • The DFS Management Console ROCKS - it's based on the Management Console (MMC) 3.0 and is just great. E.g. it provides more help and a action pane.
  • With DFS-Namespace (DFS-N) you are able to configured preferred servers (preferred in the same site, preferred globally) and failback (prior you only had fail-over to other servers if one server wasn't available, but it wasn't failing back while the client was online).
  • DFS-Replication (DFS-R) does not replace FRS, cause FRS is still used for replicating Sysvol.
  • DFS-R provides RDC, Remote Differential Compression. RDC is providing - hold your breath - Delta Replication for Files. RDC will only replicate the changes of large files, the smalles unit to replicate is 4KB. So if you have large files where only small changes occur RDC will help you to replicate those faster with less WAN-Traffic.
  • If one of the replication partners is a Windows Server 2003 R2 Enterprise Edition RDC will also be able to detect delta changes between files, such as cutting two slides out of a PowerPoint-Presentation and pasting them into another one.
  • DFS-R provides replication Schedules + Replication Bandwidth. So you are able to select which times replication should occur and which Bandwidth (in average) should be used during replication.
 
I did some testing with DFS and especially RDC - and I just love it. I kept the Replication Schedule to always, and with LAN speed I was unable to figure out the delay when accessing two different shares, it appeared as the same share, even when I made changes to large files. RDC ROCKS!!

Published Thu, Nov 3 2005 5:16 by Ulf B. Simon-Weidner

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Comments

# re: Windows Server 2003 R2: DFS out of the Branch Office Solutions@ Tuesday, November 08, 2005 6:53 AM

Hi Ulf,

In your testing, how many files were you replicating? What would/should the target usage scenario for RDC be? By this, I mean should you be replicating thousands of files or hundreds of files? What's the scalability on DFS-R? I've not done testing on a large scale, but am interested in hearing your opinion on where DFS-R may not be appropriate and where it would be appropriate.

Thanks.

-matt

Ulf B. Simon-Weidner

# re: Windows Server 2003 R2: DFS out of the Branch Office Solutions@ Tuesday, November 15, 2005 12:07 AM

Small correction Ulf. RDC works w/o issue across standard edition servers using DFS-R on both sides. You get the goodness of RDC in most cases. The one feature in R2 that requires ent edition on one side is cross-file RDC (the feature by which we take parts of one file and use them to construct another).

Ulf B. Simon-Weidner