FlexLevel: A novel NAND flash storage system design for LDPC latency reduction

LDPC code is introduced in NAND flash memory to handle high BER (bit error rate) incurred by technology scaling. Despite strong error correction capability, LDPC decoding induces long NAND flash read latency. In this work, we propose FlexLevel - a robust NAND flash storage system design to improve data reliability and read efficiency affected by the LDPC operations. FlexLevel first reduces BER by enlarging noise margins via Vth (threshold voltage) level reduction. It reduces the sensing levels of LDPC but also causes loss of storage capacity. To compensate this capacity loss with minimum impact on read performance, FlexLevel identifies the data with high LDPC overhead and only applies the V
th
level reduction technique to those data. Experimental results show that compared with state-of-the-art, FlexLevel can achieve up to 33% read speedup with very moderate capacity loss.