External disk sleep

I have an external disk connected via Firewire. I want to tell the system to NEVER sleep this disk.
Howard S Shubs wrote on :

I know I've seen this in either MacWorld or MacAddict, but I can't seem to find it right now.

I have an external disk connected via Firewire. I want to tell the system to NEVER sleep this disk. The Energy Saver control panel only handles the internal disk. There's some way to give the system such options for additional drives, though. Does anyone remember what it is?