Maximizing the Availability of Replicated Services in Widely Distributed Systems Considering Network Availability

Availability is an important issue in distributed environments that promise to provide quality of services and thus the mechanisms to improve data or service availability is critical to ensure such quality of service. Replication schemes have been widely used to improve data or service availability. In addition to the number of replicas, the location of the replicas also impacts the data availability. In this paper, we consider the impact of node and network link failures on the availability of replicated data and services. Efficient replica allocation algorithms with runtime of O(K|V|²) are developed to improve data availability, where K is the predetermined number of replica and |V| is the number of nodes in the system. Experimental studies have been conducted to evaluate how effective the proposed replica allocation algorithms on improving the availability of replicated data or services. The results show that the two proposed solutions are effective on enhancing system availability, especially when the number of replicas is small.