Evaluation of availability of cluster distributed disaster tolerant systems for control and information processing based on a cluster quorum

Control and information processing systems, which often executes critical functions, must satisfy requirements not only of fault tolerance, but also of disaster tolerance. Cluster architecture is reasonable to be applied to provide disaster tolerance of these systems. In this case clusters are separate control and information processing centers united by means of communication channels. Thus, clusters are a single hardware resource interacting with each other to achieve system objectives. Remote cluster positioning allows ensuring system availability and disaster tolerance even in case of some units' failures or a whole cluster crash. A technique for evaluation of availability of cluster distributed systems for control and information processing based on a cluster quorum is presented in the paper. This technique can be applied to different cluster distributed control and information processing systems, claimed to be based on the disaster tolerance principles. In the article we discuss a communications satellite system as an example of a cluster distributed disaster tolerant control and information processing system. Evaluation of availability of the communications satellite system is provided. Possible scenarios of communications satellite system cluster-based components failures were analyzed. The analysis made it possible to choose the best way to implement the cluster structure for a distributed control and information processing system. (paper)