Microsoft's distributed file system (DFS) provides a way for users and administrators to have a single, unified view of files spread over many servers in the organization.
DFS allows for easier file management and lets users find things more readily. However, there are some limits to DFS' capacity that can hamper its usefulness.
Although the problems involve running out of capacity, this isn't a matter of physical storage, and adding storage devices usually won't help.
Instead, the problem revolves around built-in limits with DFS and Windows itself. One of the frequent troublemakers, for example, is the 260-character limit in pathnames imposed by Windows APIs. A poorly planned DFS implementation can easily exceed that limit, resulting in an error message rather than a file retrieval.
To mitigate problems, Microsoft recommends several techniques when designing a DFS file system.
- Limit comments. You can comment the root target or link in a DFS system, which is handy for keeping track of the complex structure of a DFS. However, those comments count against length limits, so keep them as short as possible.
- Cascade namespaces. DFS namespaces are limited to 5,000 links. If you need a larger structure than that, you can create multiple namespaces within the recommended sizes and link them together. The links pointing to other links are called interlinks.
- Enable root scalability mode. Root scalability mode lets you use more than 16 root targets. This can greatly expand the size of the DFS and ease management by helping to organize the system.
Microsoft discusses the limits of DFS and workarounds in a FAQ at: http://www.microsoft.com/windowsserver2003/techinfo/overview/dfsfaq.mspx
About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.
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