CacheCOW: providing QoS for storage system caches

Managed hosting and enterprise wide resource consolidation trends are increasingly leading to sharing of storage resources across multiple classes, corresponding to different applications/customers, each with a possibly different Quality of Service (QoS) requirement. To enable a storage system to meet diverse QoS requirements, we present two algorithms for dynamically allocating cache space among multiple classes of workloads. Our algorithms dynamically adapt the cache space allocated to each class in response to the observed response time, the temporal locality of reference, and the arrival pattern for each class. Using trace driven simulations collected from large storage system installations, we experimentally demonstrate that the algorithms not only meet the QoS requirements, but also increase the throughput by achieving a higher hit rate whenever feasible.