Windows DFS is supposed to do all sorts of useful things in a domain, like reducing mapped drives, acting as an online backup in the event of downed servers, and caching files locally so WAN usage doesn’t spike (see Microsoft’s DFS Infrastructure marketing info). for Windows DFS basics and setup information: WindowsNetworking.com has a good article explaining Microsoft’s DFS terminology and function, plus I don’t feel like explaining everything and creating the screenshots like they offer.

Like all “infrastructure” tools it adds complexity to the system and requires extra resources to function correctly. In particular, Windows DFS buffers all files that are changed locally before it copies them over the other replicas. Unfortunately, since DFS (as of Windows 2003 SP1) copies entire files and not just the changes it uses a lot of drive space as a buffer - and it can’t even replicate files that may exceed the buffer size. The default buffer size on windows 2000 and 2003 Server is 4GB, so consider not replicating the files causing this problem. After all, pushing 4GB+ files around the WAN isn’t exactly efficient for DFS or any system.

To bump up the DFS buffer size, first make sure you have enough disk space locally to allocate it to the buffer and enough disk space remotely to accommodate the multi-GB mile you’re about to send. Then open regedit and navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NtFrs\Parameters\. Change the value of the DWORD “Staging Space Limit in KB” to accommodate your largest files (remember MS still uses binary KB and MB based on multiples of 1024, instead of digital 1000x units).

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