A Resource Allocation Model for Hybrid Storage Systems

Providing QoS guarantees for hybrid storage systems made up of both solid-state drives (SSDs) and hard disks (HDs) is a challenging problem. Since HDs and SSDs have widely different IOPS capacities, it is not sensible to treat the storage system as a monolithic black box, instead a useful QoS model must necessarily differentiate the IOs made to different device types. Traditional storage resource allocation models have largely been designed to provide QoS for a single resource type, and result in poor utilization and fairness when applied to multiple coupled resources. In this paper, we present a new resource allocation model for hybrid storage systems using a multi-resource framework. The model supports reservations and shares for clients sharing the storage system. Reservations specify the minimum throughput (IOPS) that a client must receive, while shares reflect its weight relative to other clients that are bottlenecked on the same device. We present a formal multi-resource allocation model to allocate IOPS to clients, together with an IO scheduling algorithm to maximize system throughput. The model and algorithms are validated with empirical results.