A standby-sparing technique with low energy-overhead for fault-tolerant hard real-time systems

Time redundancy (rollback-recovery) and hardware redundancy are commonly used in real-time systems to achieve fault tolerance. From an energy consumption point of view, time redundancy is generally more preferable than hardware redundancy. However, hard real-time systems often use hardware redundancy to meet high reliability requirements of safety-critical applications. In this paper we propose a hardware-redundancy technique with low energy-overhead for hard real-time systems. The proposed technique is based on standby-sparing, where the system is composed of a primary unit and a spare. Through analytical models, we have developed an online energy-management method which uses a slack reclamation scheme to reduce the energy consumption of both the primary and spare units. In this method, dynamic voltage scaling (DVS) is used for the primary unit and dynamic power management (DPM) is used for the spare. We conducted several experiments to compare the proposed system with a fault-tolerant real-time system which uses time redundancy for fault tolerance and DVS with slack reclamation for low energy consumption. The results show that for relaxed time constraints, the proposed system provides up to 24% energy saving as compared to the time-redundancy system. For tight deadlines when the time-redundancy system can tolerate no faults, the proposed system preserves its fault-tolerance but with about 32% more energy consumption.