PEVA: A Page Endurance Variance Aware Strategy for the Lifetime Extension of NAND Flash

With aggressive scaling and multilevel cell technology, the reliability of NAND flash continuously degrades. The lifetime of NAND flash is highly restricted by the bit error rate (BER), and error-correcting codes (ECCs) can provide only limited error correction capability to tolerate increasing bit errors. To cope with this issue, a novel page endurance variance aware (PEVA) strategy is proposed to extend the lifetime of NAND flash based on the experimental observations from our hardware-software codesigned experimental platform. The experimental observations indicate that the BER distribution of retention error shows distinct variances in different pages. The key purpose of PEVA is to exploit the lifetime potency of every page in a block by introducing fine-grained bad page management instead of coarse-grained bad block management (BBM). The experimental results show that the PEVA can extend the lifetime of 2×-nm NAND flash by 9.8× compared with the conventional BBM and that there is at most an 8.7% degradation in writing speed compared with the traditional sector mapping technology. In addition, the maximum writing response time increased by at most 5.9% during the operation of the PEVA strategy.