Computing replica placement in distributed systems

The authors investigate the design of a replica management system (RMS) which allows a programmer to specify the quality of service required for individual replicated objects in terms of availability and performance. From the quality of service specification, information about the replication protocol to be used, and data about the characteristics of the underlying distributed system, the RMS computes an initial placement and replication level for the object. As machines and communications systems are detected to have failed or recovered, the RMS can be reinvoked to compute an updated mapping of replicas which preserves the desired quality of service. Preliminary simulation of the authors RMS shows that its placement algorithm gives consistent improvements in the availability of a replicated service than simply placing replicas on nodes at random, as is done in most distributed systems