Abstract: The primary/backup process is commonly used in heterogeneous distributed systems with fault tolerance.This paper proposed a heterogeneous distributed hybrid model with fault tolerance. Compared with the traditional heterogeneous distributed scheduling models, this model can simultaneously schedule both periodical and aperiodical tasks.Three fault tolerant scheduling algorithms based on this model were presented: SSA(Schedulability Scheduling Algorithm) algorithm aimed at schedulability, RSA(Rcliability Scheduling Algorithm) algorithm aimed at reliability and BSA (Balanced Scheduling Algoritlnn) algorithm aimed at load equalization. These algorithm can simultaneously process real-time tasks in demand of periodical or aperiodical fault-tolerance in heterogeneous systems. And they can guarantee that real-time tasks could complete befor the cut off time even if some node of the system fails. Finally, this paper analyseds the algorithms in five ways; schedulability, reliability cost, load equalization, number of periodical and aperiodical tasks, cycle and granularity. Experiment results show that the algorithms have advantages and disadvantages respectively, so they should be chosen according to the characteristics of a specail heterogeneous system.

Key words: Primary/backup copy, Heterogeneous distributed, Periodic and aperiodic task, Load balancing, Reliability,Schedulability