A cluster-based ultrareliable architecture is presented, offering synchronization and system functionality comparable to that of fully connected systems, with reduced system overhead. A reliability model considering the distribution of concurrent faults across the system clusters is shown to increase the accuracy of reliability and system fault-tolerance estimates. The hybrid fault model, which classifies faults based on their behavior, further improves reliability estimates and enhances the fault handling capability of each cluster. Linear growth in cluster reliability with respect to cluster size is possible, as are refinements in the convergence and consistency algorithms for synchronization. © 1992 IEEE.