Semi-RAID: A reliable energy-aware RAID data layout for sequential data access

In this paper, we propose an alternative RAID data layout, Semi-RAID (S-RAID), for the kind of application that exhibits a sequential data access pattern. The data layout of S-RAID uses a grouping strategy that makes only part of the whole array active and puts the rest of the array into standby mode. In this way S-RAID can greatly reduce the power consumption and improve the reliability while still satisfying the I/O requirements of the application. We have shown that transforming a traditional RAID 5 into S-RAID 5 makes average mean time to failure (MTTF) 8 times as long as before, and reduces the power consumption to 74% in a 5-disk configuration. In a typical video surveillance system that has 25 disks, S-RAID may reduce the power consumption to nearly 15% in the best case. The performance of S-RAID is evaluated and proved to be sufficient for the workloads it is optimized for. Possible optimization for other workloads has also been given at the end of the paper.