I have a server cabinet that has 2x 120mm 240v fans mounted in the roof. They are far too noisy to have running at full speed during office hours, so I am looking for a way of controlling the fan speed via the server itself. The plan is to replace the fans with 12v fans, and somehow run them from the USB port of the server and use some form of software to control the speed based on the temperature of the server. Is this possible? Should I instead use some form of 240v thermostat and just run the fans based on the ambient temperature? Suggestions?