Microsoft has made significant investments in their Windows storage initiative. A key measure of such an initiative is the ongoing investment in the new features in DFS in Windows Server 2003. DFS is a cornerstone of Microsoft's storage strategy as can be seen in the strategy guide on Deploying File Servers (available at the Microsoft web site at the link below), which contains extensive information for planning and implementing a DFS-based solution.
Here are some technical highlights on the new DFS features and how they can provide long-term benefits to customers.
The first benefit is the support for large namespaces. In Windows 2000, an administrator was restricted to a documented limit of about 10,000 links to a single standalone DFS root. In most small to medium sized installations, this is not an issue. (I do know of one customer who currently has over 50,000 links under a single root in their Windows 2000 namespace.) However, in Windows Server 2003, the documented limit is upwards of 50,000. Large link counts in a single root have been tested and have seen acceptable performance.
The second benefit is in the number of DFS roots that can be hosted on a single server. While Windows 2000 restricted an administrator to a single root per server, Windows Server 2003 removes this limitation. While the Standard Edition can only host one root per machine, the Enterprise Edition and the Datacenter Edition can host multiple roots to a single machine. This eliminates the burden of having the administrator purchase 5 servers to host 5 different roots. Of course, the administrator must provide high availability of the multiple roots on a single machine by either clustering or using Domain-based roots.
DFS is now more site-aware than before. Currently, a DFS client selects a target that is "closest" to it based on the client's IP subnet and the IP subnet of all replica targets. If there is no target in the same site as the client, the client will randomly select any target that is not in the same site. For example, consider a client that is located in Houston and the replica targets are in Houston, Dallas, and New York. If the server in Houston is unavailable, then the client is equally likely to go to Dallas or New York to retrieve the data. The benefit that Windows Server 2003 adds is that now the client can be directed to alternate targets based on the lowest connection cost if no same-site targets are available.
These and other new features make DFS on the Windows platform a viable base upon which to form a long-term strategy for highly available file servers.
About the author
Sri Seshadri is a MCSE and MCT in NT 3.51, NT 4, and W2K. For more than a decade Sri has been a consultant at DCSS specializing in Windows NT/2000 enterprise-related design, implementation, and support of large infrastructure projects. You can contact Sri at firstname.lastname@example.org