The effect of the primary site approach for fault tolerance on the response time is studied. In the primary site approach, the service to be made fault tolerant is replicated at many nodes, one of which is designated as primary and the others as backups. All the requests for operations on the data object are sent to the primary site. The primary fails, one of the backups takes over as primary. The primary site periodically checkpoints its state on the backups. An analytical model for studying the average response time of the primary site system and analyzing the effects of the checkpointing frequency and the degree of replication on the response time is presented. This model is used to compare the response time of the system to that of a system without any fault tolerance.
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