Improving Small File Performance in Object-based Storage (CMU-PDL-06-104)

This paper proposes architectural refinements, server-driven metadata prefetching and namespace flattening, for improving the efficiency of small file workloads in object-based storage systems. Server-driven metadata prefetching consists of having the metadata server provide information and capabilities for multiple objects, rather than just one, in response to each lookup. Doing so allows clients to access the contents of many small files for each metadata server interaction, reducing access latency and metadata server load. Namespace flattening encodes the directory hierarchy into object IDs such that namespace locality translates to object ID similarity. Doing so exposes namespace relationships among objects (e.g., as hints to storage devices), improves locality in metadata indices, and enables use of ranges for exploiting them. Trace-driven simulations and experiments with a prototype implementation show significant performance benefits for small file workloads. Acknowledgements: We thank the members and companies of the PDL Consortium (including APC, EMC, Equallogic, Hewlett-Packard, Hitachi, IBM, Intel, Microsoft, Network Appliance, Oracle, Panasas, Seagate, Sun, and Symantec) for their interest, insights, feedback, and support. We also thank Intel, IBM, Network Appliances, Seagate, and Sun for hardware donations that enabled this work. This material is based on research sponsored in part by the National Science Foundation, via grant #CNS-0326453, by the Air Force Research Laboratory, under agreement number F49620–01–1–0433, and by the Army Research Office, under agreement number DAAD19–02–1–0389. James Hendricks is supported in part by an NDSEG Fellowship, which is sponsored by the Department of Defense.