If you have have a slow DFS server which you only want to be available when the primary DFS server is down, you can use Target Priority to set the priority of the slow server to GlobalLow.
To do this:
2. Open a CMD.EXE window.
3. Type the following command and press Enter:
dfsutil /path:<DFSLinkPath> /TargetPriority /Server:<SlowServerName> /Share:<ShareName> /Set /PriorityClass:GlobalLow