As I mentioned in a somewhat related post I've completed many CIFS migrations using nothing more than robocopy and vbscripts to conrol the jobs. We are currently in the midde of a migration from two Celerras with roughly 80TB of data on CX and DMX arrays. We also have DFS in place for roughly 10% of the shares and those are easy to migrate: 1) for each DFS link create an equivalent share on the filer and robocopy the data over (we typically start the inital copy a week ahead of the cutover). 2) re-run the robocopy job on a periodic basis to keep the differential data in sync 3) on the cutover date, remove access to the source for clients (different ways to do this but the easiest in my opinion is to modify the share permissions) and kill any sessions so that no new data is written to the source during the cutover window 4) perform a final sync of the data to the target. 5) modify the DFS link to point to the new UNC path.
There are a few tricks to speed up the initial copy and the subsequent mirrors and you have think about whether you need to do any aliasing but the basic process is fairly straightforward. If you have any other specific questions feel free to ask...
