Resource allocation for primary-site fault-tolerant systems

Resource allocation for a distributed system employing the primary site approach for fault tolerance is discussed. Two kinds of systems are considered. The first consists of fault-tolerant nodes where each node has many duplicated servers. One server is the primary, which serves user requests, and the rest are backup. The second does not have fault-tolerant nodes. To tolerate node failures, each node uses other nodes as backups. When a node fails, all requests initially allocated to the node are served by one of its backups. To study the resource allocation for such systems, an approximate model for each system is developed. Using these models, efficient allocation algorithms that take into account the failure/repair rates of the system and the fault-tolerant overheads are presented. Using experimental results, it is shown that the algorithms give the optimal or suboptimal allocations. The algorithms, which incur little overhead, can improve the system performance significantly over an intuitive allocation algorithm