Scalable service differentiation in a shared storage cache

Motivated by the need to enable easier data sharing and curb rising storage management costs, storage systems are becoming increasingly consolidated and thereby shared by a large number of users and applications. In such environments, service differentiation becomes increasingly important. Since caching is a fundamental and pervasive technique employed to improve the performance of storage systems, providing differentiated services from a storage cache is a crucial component of the entire end-to-end QoS solution. In this paper we discuss a QoS architecture for a shared storage proxy cache which can provide long-term hit rate assurances to competing classes. The proposed architecture consists of three components: (a) per-class feedback controllers that track the performance of each class, (b) a fairness controller that allocates excess resources fairly in the case when all goals are met, and (c) a contention resolver that decides cache allocation in the case when at least one class does not meet its target hit rate. We compare the performance of various feedback per-class controllers, and provide guidelines for designing QoS mechanisms for such a dynamic environment.