The Redundant radioserver continuously checks the presence of the Main server.
If it senses that the Main server is no longer responding, it will switch on and take up all Master’s duties. This part is known by everybody, and here comes the hidden part: if the Redundant radioserver does not sense any presence of the Main server in 31 days continuously, it will stop the service. So, the Main server should be online at least once per month for a time period long enough so that the Redundant radioserver could sense the presence of the Master.
Resume: do not leave the redundant server running forever alone, provide him with a company 😉