HLC: Software-based half-level-cell flash memory

In recent years, flash memory has been widely used in embedded systems, portable devices, and high-performance storage products due to its non-volatility, shock resistance, low power consumption, and high performance natures. To reduce the product cost, multi-level-cell flash memory (MLC) has been proposed; compared with the traditional single-level-cell flash memory (SLC) that only stores one bit of data per cell, each MLC cell can store two or more bits of data. Thus MLC can achieve a larger capacity and reduce the cost per unit. However, MLC also suffers from the degradation in both performance and reliability. In this paper, we try to enhance the reliability and reduce the product cost of flash-memory based storage devices from a totally different perspective. We propose a half-level-cell (HLC) management scheme to manage and reuse the worn-out space in solid-state drives (SSDs); through our management scheme, the system can treat two corrupted pages as a normal page without sacrificing performance and reliability. To the best of our knowledge, this is the first research that reclaims free space by reviving the corrupted pages. The experiment results show that the lifetime of SSD can be extended by 48.54% for the trace of general users applications with our proposed HLC management scheme.