On endurance of erasure codes in SSD-based storage systems

The wear-out of flash-based Solid-State Drives (SSDs) is a main concern that significantly affects their reliability. One major parameter that accelerates SSD wear-out is the number of write-cycles committed to flash chips. The number of write-cycles in SSD-based disk subsystem is highly dependent on the erasure code implemented in Redundant Array of Independent Disks (RAIDs). In this paper, we investigate the impact of erasure codes and the configuration of storage subsystems (i.e., the number of disks participated in the RAID array and stripe unit size) on the endurance of storage systems. The number of write-cycles is considered as a metric to evaluate the endurance of storage system. We evaluate the endurance of four different well-known erasure codes, i.e., Reed-Solomon, EVENODD, RDP, and X-Code, employed in SSD-based RAID systems. In the evaluation, the number of write-cycles is measured with respect to the number of disks, stripe unit size, and request size using trace-driven simulation. The simulation results show that Reed-Solomon provides the lowest number of write-cycles due to the optimal dependency between data and parities in its coding. The results also demonstrate that EVENODD and RDP impose the highest number of write-cycles when using the high number of disks with large stripe unit size. These results recommend designing erasure codes with minimum dependency between data and parities as this minimum dependency provides optimal number of write-cycles.