Hi
First of all, you should understand how Telemac works. When you run a simulation, a temporary directory is used to store all the file required to run the simulation. The result is also generated in this temporary directory and filled all along the simulation. At the end of the simulation, the result is copied with the given result name, relatively to the palce you run the simulation and the temporary is erased.
So specify a location on an external disk is possible but this doesn't change the problem of the temporary storage...
You could also execute Telemac on the temporary storage but then you could slow down your computation as access to external drive are slower...
Regards