Quasi-nonvolatile SSD: Trading flash memory nonvolatility to improve storage system performance for enterprise applications

This paper advocates a quasi-nonvolatile solid-state drive (SSD) design strategy for enterprise applications. The basic idea is to trade data retention time of NAND flash memory for other system performance metrics including program/erase (P/E) cycling endurance and memory programming speed, and meanwhile use explicit internal data refresh to accommodate very short data retention time (e.g., few weeks or even days). We also propose SSD scheduling schemes to minimize the impact of internal data refresh on normal I/O requests. Based upon detailed memory cell device modeling and SSD system modeling, we carried out simulations that clearly show the potential of using this simple quasi-nonvolatile SSD design strategy to improve system cycling endurance and speed performance. We also performed detailed energy consumption estimation, which shows the energy consumption overhead induced by data refresh is negligible.