On designing endurance aware erasure code for SSD-based storage systems

Erasure codes are applied in both HDD and SSD storage systems to improve the reliability. The design of erasure codes for SSD-based systems should be performed with respect to a specific feature of SSDs, i.e., endurance. Endurance is defined as the number of Program/Erase (P/E)-cycles that one SSD can endure for reliable operation. The common metric for comparing the endurance of two systems is the number of P/E-cycles, which is yielded by time-consuming simulations. This paper proposes two new metrics called DPD-factor and GDP-pattern, for comparing the effect of erasure codes on the endurance of systems based on their encoding designs, without simulation. With respect to the endurance, EA-EO is designed as the modification of EVENODD with smaller DPD-factor. The endurance of EVENODD and EA-EO are compared regarding the system configurations: the size of stripe unit, the number of disks, and the sizes of request. The results of comparison show that the best configurations of system for enhanced endurance are: 1) a large number of disks are applied in systems, or 2) the size of request is equal to the stripe unit size. Furthermore, it concludes that a code with smaller DPD-factor and a sequential GDP-pattern can provide higher endurance for systems.