Dfs vs. FRS

Admin wants to maintain snappy performance with user profiles and home folders with a Windows 2003 network upgrade.

Bill: We have three sites that are their own Windows NT 4.0 domain and subnet. One connection between sites is a 11Mbps WLAN, and the other a 2Mbps fibre link. Some staff remain at one site and others move among all three.

We are upgrading to Windows Server 2003 and would like to change to a single domain over the entire company and sites. We will have a DC at each site. We know this can be done, but what I want is some assistance with user profile and home folder management.

Using Distributed File System and File Replication Service, can we maintain all user profiles and home folders at each site? What if a user creates a 100MB file at one site? Might this cause congestion over the WAN links?

This may be a very simple task to get what we want, but I greatly appreciate any assistance you can lend me.

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Ben: It is certainly possible to maintain local copies of user home folders and profiles on different servers, then use Dfs to point the users at local copies of the files. This localization relies on Active Directory sites defined in DNS, and properly configured IP subnet objects, so make sure your site configuration is correct and that all Service Locator (SRV) records are present in DNS. Also, Windows Server 2003 Dfs does a much better job of corralling Dfs users into the correct site. Windows 2000 sometimes points Dfs users at a randomly selected site rather than the local site.

Using FRS to replicate the files is also possible, but there are some drawbacks. FRS is a perfectly acceptable replication engine for the small files in Sysvol, but when you ask it to replicate large volumes of data across slow or congested WAN links, the results can get a little problematic.

Take that 100MB file you mentioned as an example. Not only would FRS replicate the file when it's first created, each time a user modifies the file in any way, FRS will replicate a full copy of the file again. If a user opens and closes the file a dozen times in 10 minutes, then 10 copies of the file will replicate across that 2Mb link. FRS is a little simpler to configure in Windows Server 2003 because you can define custom replication topologies, but the engine just isn't intended for moving many, many MBs of files.

One way to avoid the problem of replicating very large files is to impose fairly drastic quotas on home folders and profiles. This forces users to save their data files in the production environment somewhere, such as their department folder. You can argue that this is the best use of storage, but users often want their own little cubbyhole and they don't believe that you can protect their privacy in a folder under the main department folder. Also, it tends to defeat the advantage of using local copies of files via Dfs.

Some organizations have tried to make FRS work for large volumes and then turned around and deployed a third-party solution for replication. Here are some examples (and, by no means, extensive):

The other thing to watch out for in Dfs is file locking. If User A opens a file on one server and User B opens the same file on a different server, then the last user to save the file will overwrite the work done by the other user. For this reason, Dfs works well for user home folders and profiles, but don't use it for common data. And keep the file locking in mind if you come in as an administrator and make changes to profiles or home folders while users are logged on.

Hope this helps.

About the Author

Contributing Editor Bill Boswell, MCSE, is the principal of Bill Boswell Consulting, Inc. He's the author of Inside Windows Server 2003 and Learning Exchange Server 2003 both from Addison Wesley. Bill is also Redmond magazine's "Windows Insider" columnist and a speaker at MCP Magazine's TechMentor Conferences.


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