Performance and reliability of NAND flash/SCM hybrid SSD during write/erase cycling

This paper describes the comprehensive analysis on the performance of NAND flash/storage-class memory (SCM) hybrid solid-state drive (SSD) during write/erase (W/E) cycling for various applications. Since bit-error rate (BER) increases by cycling, increasingly stronger ECC should be applied, which results in longer ECC calculation time. Both program/erase latencies of the NAND flash memory and ECC calculation time change during W/E cycling and have complex effects on the SSD performance. By assuming that the reliability of SCM simultaneously degrades with NAND, the SSD performance is also evaluated by the transaction-level simulator. Three key results are derived: (i) the error-correction latency strongly impacts both NAND-only and hybrid SSD´s performance, (ii) the SSD performance with error-correction is sensitive to the workload and (iii) reliability requirements of NAND and SCM are defined for various applications. The BER of SCM can be 1% at maximum.