Storage accounts for a significant amount of a data center’s ever increasing power budget. As a consequence, energy consumption has joined performance and reliability as a dominant metric in storage system design. In this paper, we show that the structure of an erasure code— which is generally used to provide data reliability—can be exploited to save power in a storage system. We define a novel technique in power-aware systems called poweraware coding and present generic techniques for reading, writing and activating devices in a power-aware, erasurecoded storage system. While our techniques have an effect on energy consumption, fault tolerance and performance, we focus on a few examples that illustrate the tradeoff between power efficiency and fault tolerance. Finally, we discuss open problems in the space of poweraware coding. 1

Deduplication on is rarely used on primary storage because of the disk bottleneck problem, whichresultsfromtheneed to keep an index mapping chunks of data to hash values in memory in order to detect duplicate blocks. This index grows with the number of unique data blocks, creating a scalability problem, and at current prices the cost of additional RAM approaches the cost of the indexed disks. Thus, previously, deduplication ratios had to be over 45 % to see any cost benefit. The HANDS technique that we introduce in this paper reduces the amount of in-memory index storage required by up to 99 % while still achieving between 30 % and 90 % of the deduplication of a full memory-resident index, making primary deduplication cost effective in workloads with a low deduplication rate. We achieve this by dynamically prefetching fingerprints from disk into memory cache according to working sets derived from access patterns. We demonstrate the effectiveness of our approach using a simple neighborhood grouping that requires only timestamp and block number, making it suitable for a wide range of storage systems without the need to modify host file systems. 1.