Tips and Tricks

DFS to the Rescue

The power of this simple, useful tool is more evident when used during server consolidations or migrations.

Many organizations use Windows’ Distributed File System (DFS) to replicate certain shared folders or to make accessing user directories more straightforward (after all, \\DFS\ Users\Don is easier to remember than \\NT254LAS\DJONE$). But DFS can also be a useful tool during server migrations and server consolidation.

The idea behind DFS is to allow users access shared folders using a consistent namespace that has nothing to do with where the data actually resides. So a friendly UNC, such as \\DFS\Projects\Marketing\BigSale might really point to a shared folder named \\ServerA\MktSaleShare.

Ease-of-use is nice, but DFS has some internal trickery going on that makes it even more useful. For instance, DFS doesn’t act as a gateway for clients; it simply provides a referral. In other words, clients who access \\DFS\Projects\Marketing\BigSale hit the DFS server, and are redirected to \\ServerA\ MktSaleShare. Because of that redirection, DFS can provide references to any shared data, not just Windows shared folders. For example, \\ServerA\MktSaleShare might really be a NetWare server or Linux file server; clients don’t care, so long as they have the software necessary to access that type of data.

During a migration, you can use DFS to maintain a consistent namespace: After you migrate the data in \\ServerA\MktSale Share to a Windows server, simply update the reference in DFS to point to the new Windows-based shared folder (which might be \\WinServer2\Marketing5). Users can continue to access the same UNC they did before, and DFS handles the redirect to the new server, all behind the scenes.

DFS can serve a similar purpose during a server consolidation. By having users access DFS-based UNCs, rather than accessing server UNCs directly, you can play the old shell game behind the scenes: Users get their data from \\DFS\Users\DonJ, even though today that data physically resides at \\NTServer\Don and tomorrow it’ll be moved to \\Win2003A\DonJ. Shuffle files and shared folders around all you want—DFS maintains an orderly façade and prevents you from having to notify users of the change.

DFS can also provide easier access to frequently used Read-only files (such as Microsoft Office network installation points). A single DFS UNC can point to multiple, identical UNCs on the back end. Since DFS is site-aware, users are directed to the UNC that’s physically closest to them whenever possible. So all of your Office users can get their software from \\DFS\Applications\Office, and they’ll be automatically referred by DFS to the nearest copy.

One caveat: Don’t put a copy (called a DFS replica) on the server that’s actually hosting the DFS root. DFS has a hardcoded preference for replicas on the root, and users will always be directed to that copy, no matter how many others exist on the network.

Installing DFS
Make sure your clients have the latest DFS client installed, and you’ll get the best performance. Doing so can be tricky, though, because the DFS client is usually embedded in other software. On Windows 9x and NT systems, install the Directory Services Client; Windows 2000, XP and Windows Server 2003 contain the latest code either in the base OS or in the most recent service pack.

The one point of failure in this system, of course, is the DFS root server: If it goes down, it can’t hand out referrals to clients, so the whole system collapses. You can get better odds on a stable DFS environment by installing the DFS root on a small Windows cluster. DFS is natively built for clustering, and the cluster will ensure that even a fairly massive hardware failure won’t take your DFS system offline for long.

About the Author

Don Jones is a multiple-year recipient of Microsoft’s MVP Award, and is an Author/Evangelist for video training company Pluralsight. Don is also a co-founder and President of PowerShell.org, a community dedicated to Microsoft’s Windows PowerShell technology. Don has more than two decades of experience in the IT industry, and specializes in the Microsoft business technology platform. He’s the author of more than 50 technology books, an accomplished IT journalist, and a sought-after speaker and instructor at conferences worldwide. Reach Don on Twitter at @concentratedDon, or on Facebook at Facebook.com/ConcentratedDon.

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