Warm Standby in Hierarchically Structured Process-Control Programs

We classify standby redundancy design space in processcontrol programs into the following three categories: cold standby, warm standby, and hot standby. Design parameters of warm standby are identified and the reliability of a system using warm standby is evaluated and compared with that of hot standby. Our analysis indicates that the warm standby scheme is particularly suitable for long-lived unmaintainable systems, especially those operating in harsh environments where burst hardware failures are possible. The feasibility of warm standby is demonstrated with a simulated chemical batch reactor system. Zndex Terms-Fault tolerance, process-control, standby replacement, replication, knowledge representation, reliability assessment.