Modeling the Physical Characteristics of Nand Flash Memory

Flash memory has gained tremendous popularity in recent years. A variant of flash, referred to as NAND flash, is widely used in consumer electronics products, such as cell-phones and music players while NAND flash based Solid-State Disks (SSDs) are increasingly displacing hard disk drives as the primary storage device in laptops, desktops, and even data centers. Computer architects have recently begun exploring the use NAND flash, from SSD organizations to disk caches and even new flash-based server architectures. In order to study this design space, architects require simulation tools that can provide detailed insights into the behavior of flash memory. This thesis presents two such tools that model two important characteristics of NAND flash: power consumption and endurance. The first tool, called FlashPower, is a microarchitecture level modeling tool that provides a detailed analytical power model for Single-Level Cell (SLC) based NAND flash memory. FlashPower estimates the power consumed by a NAND flash memory chip during its various operating modes. We have validated FlashPower against published chip power measurements and show that they are comparable. Results from a design space exploration using FlashPower indicate that the values of bits being read or written into NAND flash memory have a significant impact on energy dissipation. The second tool, called Flash EnduraNCE (FENCE), models the endurance characteristics of NAND flash and captures the impact of stress and recovery on NAND flash memory cells. Using FENCE, we show that the recovery process, which prior studies on flash based SSDs have not considered, significantly boosts endurance. Using a set of real enterprise workloads, we show that this recovery process allows for orders of magnitude higher endurance than those given in datasheets. Our results indicate that, under realistic usage conditions, SSDs that use standard wear-