The effectiveness of adding standby redundancy at system and component levels

The effect of adding standby redundancy at the system and component levels is studied. Compared with parallel redundancy, standby redundancy is both easier to implement and more essential in the study of maintenance policies. However, standby redundancy at the component level is not always better than that at the system level, whereas it is always better for parallel redundancy. It is shown that for a series (parallel) system, standby redundancy is more effective at the component (system) level. A simple proof is given.<>