fan *
As standard, Humax chose to minimise noise over longevity. The internal temperature is assumed from the reporting built into the HDD, and the fan remains off until the temperature gets critical... then it comes on full blast (very audible) and gradually throttles back as the temperature falls. This results in the system temperature oscillating between extremes, and this isn't very good for the HDD (or the system).
fan is one of the early packages, created specifically to address the sudden onset of fan noise, but also the better regulation of cooling is good for longevity. The user sets a constant minimum fan speed (eg 30%) so the fan never turns off (but can increase from that if necessary). Low fan speeds are barely audible (the HDD makes a constant noise anyway), and the constant air flow (if set high enough) prevents the 'turbo' ever kicking in.