Code-M: A non-MDS erasure code scheme to support fast recovery from up to two-disk failures in storage systems

In this paper, we present a novel coding scheme that can tolerate up to two-disk failures, satisfying the RAID-6 property. Our coding scheme, Code-M, is a non-MDS (Maximum Distance Separable, tolerating maximum failures with a given amount of redundancy) code that is optimized by trading rate for fast recovery times. Code-M is lowest density and its parity chain length is fixed at 2C - 1 for a given number of columns in a strip-set C. The rate of Code-M, or percentage of disk space occupied by non-parity data, is (C - 1)/C. We perform theoretical analysis and evaluation of the coding scheme under different configurations. Our theoretical analysis shows that Code-M has favorable reconstruction times compared to RDP, another well-established RAID-6 code. The quantitative comparisons of Code-M against RDP demonstrate recovery performance improvement by a factor of up to 5.18 under single disk failure and 2.8 under double failures using the same number of disks. Overall, Code-M is a RAID-6 type code supporting fast recovery with reduced I/O complexity.