Spatial-Locality-Aware Virtual Storage Devices with Tangible QoS Expressions

Consolidated storage service receives its momentum in the building of various IT system infrastructures because of its cost efficiency, reliability, and maintainability. Meanwhile, only when users who run their applications on the consolidated storage system have a similar or better performance experience compared to those using direct-attached storage on each server can the storage design really be widely accepted. We propose a framework in which performance of servicing requests from one user is well isolated from that for the others in such a way that each user can be regarded as being allocated an independent virtual disk (VD) of performance as specified in its service-level agreement (SLA). Three SLA expressions that we believe are most tangible to users are supported in the spatial-locality-aware framework, which we name as rent-a-disk, latency-conscious, and throughput-conscious. Our proposed I/O scheduling algorithm for implementing the three types of VDs provides strong isolation, low interference, and high fidelity of performance for each VD if SLA is not violated. Our algorithm also enables different types of VDs to cooperate with each other to improve performance for each VD as well as for the entire physical storage.