Originally posted by sbourg
Just to add an engineering complication to this, it is also true that re-radiation of that heat to the air must happen, or the brakes will fail. This radiation of heat will be proportional to the total surface area of the rotor, and that can be increased (or decreased) with drilled holes. Lots of little holes will do this best, but location to avoid any heat transfer restriction is also important.
Don't confuse radiation with convection. Drilling holes will not increase radiation effect. Heat loss by radiation will only happen if the surface "sees" a cold surface for most of the 180° hemisphere, not another hot surface. (Heat Transfer 301 class)