讲者：李永坤 副教授，中国科技大学计算机学院
时间：5 月 6 周五上午 9:00-11:00
地点：张江校区计算机楼 405
联系人：王新，xinw@fudan.edu.cn
Abstract
Parity-based RAID poses a design trade-off issue for large-scale SSD storage systems: it improves reliability against SSD failures through redundancy, yet its parity updates incur extra I/Os and garbage collection operations, thereby degrading the endurance and performance of SSDs. We propose EPLOG, a storage layer that reduces parity traffic to SSDs, so as to provide endurance, reliability, and performance guarantees for SSD RAID arrays. EPLOG mitigates parity update overhead via elastic parity logging, which redirects parity traffic to separate log devices (to improve endurance and reliability) and eliminates the need of pre-reading data in parity computations (to improve performance). We design EPLOG as a user-level implementation that is fully compatible with commodity hardware and general erasure coding schemes. We evaluate EPLOG through reliability analysis and trace-driven testbed experiments. Compared to the Linux software RAID implementation, our experimental results show that our EPLOG prototype reduces the total write traffic to SSDs, reduces the number of garbage collection operations, and increases the I/O throughput. In addition, EPLOG significantly improves the I/O performance over the original parity logging design, and incurs low metadata overhead.
Bio
Yongkun Li is an associate researcher in School of Computer Science and Technology, University of Science and Technology of China. Before that, he was a postdoctoral fellow at Institute of Network Coding, working with Prof. John C. S. Lui and Prof. Patrick P. C. Lee. He received his Ph.D. degree in Computer Science from The Chinese University of Hong Kong in August 2012, advised by Prof. John C. S. Lui, and Bachelor’s degree in Computer Science from University of Science and Technology of China in July 2008. His current research interests are in various topics including storage systems, especially NAND flash SSDs and non-volatile memory, online social networks, and graph analysis.
