Exploiting Redundancies and Deferred Writes to Conserve Energy in Erasure-Coded Storage Clusters

We present a power-efficient scheme for erasure-coded storage clusters---ECS²---which aims to offer high energy efficiency with marginal reliability degradation. ECS² utilizes data redundancies and deferred writes to conserve energy. In ECS² parity blocks are buffered exclusively in active data nodes whereas parity nodes are placed into low-power mode. (<i>k</i> + <i>r</i>, <i>k</i>) RS-coded ECS² can achieve ⌈(<i>r</i> + 1)/2⌉-fault tolerance for <i>k</i> active data nodes and <i>r</i>-fault tolerance for all <i>k</i> + <i>r</i> nodes. ECS² employs the following three optimizing approaches to improve the energy efficiency of storage clusters. (1) An adaptive threshold policy takes system configurations and I/O workloads into account to maximize standby time periods; (2) a selective activation policy minimizes the number of power-transitions in storage nodes; and (3) a region-based buffer policy speeds up the synchronization process by migrating parity blocks in a batch method. After implementing an ECS²-based prototype in a Linux cluster, we evaluated its energy efficiency and performance using four different types of I/O workloads. The experimental results indicate that compared to energy-oblivious erasure-coded storage, ECS² can save the energy used by storage clusters up to 29.8% and 28.0% in read-intensive and write-dominated workloads when k = 6 and r = 3, respectively. The results also show that ECS² accomplishes high power efficiency in both normal and failed cases without noticeably affecting the I/O performance of storage clusters.