bQueue: A Coarse-Grained Bucket QoS Scheduler

Abstract

We consider the problem of providing QoS guarantees in a clustered storage system whose data is distributed over multiple server nodes. Storage objects are encapsulated in a single logical bucket and QoS is provided at the level of buckets. The service that a single bucket receives is the aggregate of the service it receives at the nodes holding its constituent objects. The service depends on individual time-varying service demands and congestion at the physical servers. In this paper, we present bQueue, a coarse-grained scheduling algorithm that provides reservation and limit QoS for buckets in a distributed storage system, using tokens to control the amount of service received at individual storage servers. bQueue uses the max-flow algorithm to periodically determine the optimal token distribution based on the demands of the buckets at different servers and the QoS parameters of the buckets. Our experimental results show that bQueue provides accurate QoS among the buckets with different access patterns, and handles runtime demand changes in a reasonable way.