Saturation: reduced idleness for improved fault-tolerance

The authors present a technique for maximizing the redundancy level of tasks and tolerating hardware faults by majority voting in the context of a network of workstations. The idea is to compute dynamically the number of copies allocated to each task, according to the number of sites and the tasks´ criticality parameters. This technique leads to maximum utilization of the available resources in the distributed system, i.e. it reduces the idleness of resources and increases the redundancy of tasks. A reduction in fault dormancy and error latency is thus provided. This technique, called the saturation technique, is compared with similar approaches. A detailed description and the results obtained by simulation showing the advantages and the cost of implementing the saturation technique are given. The authors underline the structure of a convenient distributed operating system, including the execution model and task designation, to support the execution of multiple copies of tasks. The fault assumptions are discussed, and the different phases of a distributed scheduler are detailed.<>