Plethora: An EfficientWide-Area Storage System

Trends in conventional storage infrastructure motivate the development of foundational technologies for building a wide-area read-write storage repository capable of providing a single image of a distributed storage resource. The overarching design goals of such an infrastructure include client performance, global resource utilization, system scalability (providing a single logical view of larger resource and user pools) and application scalability (enabling single applications with large resource requirements). Such a storage infrastructure forms the basis for second generation data-grid efforts underlying massive data handling in high-energy physics, nanosciences, and bioinformatics, among others. This paper describes some of the foundational technologies underlying such a repository, Plethora, for semi-static peer-to-peer (P2P) networks implemented on a wide-area Internet testbed. In contrast to many current efforts that focus entirely on unstructured dynamic P2P environments, Plethora focuses on semi-static peers with strong network connectivity and a partially persistent network state. In a semi-static P2P network, peers are likely to remain participants in the network over long periods of time (e.g., compute servers), and are capable of providing reasonably high availability and response-time guarantees. The repository integrates novel concepts in locality enhancing overlay networks, transactional semantics for read-write data coupled with hierarchical versioning, intelligent replication for robustness. While mentioning approaches to other problems, this paper focuses on the problem of routing data request to blocks, while integrating caching and locality enhancing overlays into a single framework. We show significant performance improvements resulting from our routing techniques. ∗This research has been supported by the National Science Foundation.