Data layout for power efficient archival storage systems

Legacy archival workloads have a typical write-once-read-never pattern, which fits well for tape based archival systems. With the emergence of newer applications like Facebook, Yahoo! Flickr, Apple iTunes, demand for a new class of archives has risen, where archived data continues to get accessed, albeit at lesser frequency and relaxed latency requirements. We call these types of archival storage systems as active archives. However, keeping archived data on always spinning storage media to fulfill occasional read requests is not practical due to significant power costs. Using spin-down disks, having better latency characteristics as compared to tapes, for active archives can save significant power. In this paper, we present a two-tier architecture for active archives comprising of online and offline disks, and provide an access-aware intelligent data layout mechanism to bring power efficiency. We validate the proposed mechanism with real-world archival traces. Our results indicate that the proposed clustering and optimized data layout algorithms save upto 78% power over random placement.