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Obtaining consistent bandwidth with predictable latency from disk-based storage systems has proven difficult due to the storage system's inability to understand quality of service (QoS) requirements. In this paper, we present a feasibility study of QoS with the object-based storage device (OSD) specification. We look at OSD's ability to provide QoS guarantees for consistent bandwidth with predictable latency. Included in this paper is a description of QoS requirements of a sample application and how these requirements are translated into parameters that are then communicated to, and interpreted by, the OSD. Implementation problems lead to the failure of a hard real-time QoS model, but this failure is not due to the OSD protocol. The paper concludes with a description of how well the revision 9 OSD standard (OSDR9) is able to accommodate QoS. We provide suggestions for improving the OSD specification and its ability to communicate QoS requirements. |
