D-Code: An Efficient RAID-6 Code to Optimize I/O Loads and Read Performance

Abstract

With the reliability requirement increasingly important, RAID-6, which can tolerate any two concurrent disk failures, has been widely used in various storage systems. One class of typical RAID-6 implementations is to use Maximum Distance Separable (MDS) erasure codes. However, most existing RAID-6 MDS codes suffer from unbalanced I/O or high I/O cost, and cannot provide satisfied read performance on both normal mode and degraded mode. All these metrics are important in modern storage systems. In this paper, we propose a new RAID-6 MDS code termed D-Code to address these problems. D-Code uses a new kind of horizontal parities to increase the possibility of continuous data elements sharing the common parities in order to provide low I/O cost and good degraded read performance, while uses deployment parities to assure all parities can be evenly distributed in the last two rows in order to achieve good load balancing and good normal read performance. Our evaluations and experiments show that D-Code not only provides good load balancing and low I/O cost under different workloads, but also achieves good performance on both normal reads and degraded reads. E.g., D-Code achieves up to 21.3% and 13.5% higher read speed than RDP code and H-Code in normal mode, while gains up to 26.0% higher read speed than X-Code in degraded mode.