Availability analysis of the primary site approach for fault tolerance

The primary site approach is often used to support fault tolerance against node failures. The authors present an analytic model to evaluate the availability of a system using the primary site approach. The effect of the number of replicas and the checkpoint interval were studied using the model. The authors found that the optimal checkpoint interval is proportional to the square root of the checkpoint overhead and inversely proportional to the request arrival rate. For the degree of replication, the results depend on what kind of checkpointing scheme is used. In systems using the broadcasting scheme, it was found that there is no optimal degree of replication: increasing the degree of replication increases the availability. However, in systems using the point-to-point checkpointing scheme, an optimal degree of replication exists: increasing the degree of replication beyond this optimum decreases the availability. Although the authors only consider a single repair server in the system, the model can easily be extended to allow multiple repair servers