I always thought that Directory Links are a basic technology in Lotus Notes/Domino but in the last days I found that using directory links may be unsupported in some configurations.
In my case I worked with a customer who wanted to use roaming for a large number of users. He agreed to use the standard roaming directory which defaults to roaming. For performance reasons we decided to place the roaming data on a separate disk so we linked roaming to a directory on the other disk.
We soon found that we could no longer upgrade users to roaming users because the Admin Client failed with the error File does not exist on remote server.

A PMR was opened and the analyst soon found SPR SHEZ6Q9HTK. The bad news is that this SPR is currently on the status unsupported configuration.

I usually understand why some problems could not be fixed or are declared as unsupported configuration, but please can anybody tell me why this is an unsupported configuration (and I do not accept because it has not been tested, it is unsupported? Reference:
What are Directory Links, by Tom Duff