UC Santa Cruz

The accessibility of vital information can be enhanced by replicating the data on several sites, and employing a consistency control protocol to manage the replicas. The reliability of a replicated data object depends on maintaining a viable set of current replicas. When storage is limited, it may not be feasible to simply replicate a data object at enough sites to achieve the desired level of reliability. Regeneration approximates the reliability provided by additional replicas for a modest increase in storage costs, and is applicable whenever a new replica of a data object can be created faster than a system failure can be repaired. Regeneration enhances reliability by creating new replicas on other sites in response to site failures. Several strategies for replica maintenance are considered, and the benefits of each are analyzed using simulation and both algebraic and numeric solutions to systems of differential equations. Formulas describing the reliability of a replicated data object are presented, and closed-form solutions are given for the tractable cases. Numerical solutions, validated by simulation results, are used to analyze the tradeoffs between reliability and storage costs. The space savings attributable to regeneration are also quantified. © 1989 IEEE