EXPRESS: Exploiting Energy–Accuracy Tradeoffs in 3D NAND Flash Memory for Energy-Efficient Storage

Abstract

The density and cost-effectiveness of flash memory chips continue to increase, driven by: (a) The continuous physical scaling of memory cells in a single layer; (b) The vertical stacking of multiple layers; and (c) Logical scaling through storing multiple bits of information in a single memory cell. The physical properties of flash memories impose disproportionate latency and energy expenditures to ensure the high integrity of the data during flash memory writes. This paper experimentally explores this disproportionality on state-of-the-art commercial 3D NAND flash memories and introduces EXPRESS—a technique for increasing the energy efficiency of flash memory writes by exploiting the premature termination of the flash write operations. An experimental evaluation shows that EXPRESS reduces energy expenditures by 20–50%, relative to the traditional flash writes, at the cost of a minimal loss in the data integrity (<1%). In addition, we evaluate the effects of the page-to-page variability, program–erase cycling, and data retention on the implementation of EXPRESS, and we propose enhancements to counter these effects.