Over-Clocked SSD: Safely Running Beyond Flash Memory Chip I/O Clock Specs

This paper presents a design strategy that enables aggressive use of flash memory chip I/O link over-clocking in solid-state drives (SSDs) without sacrificing storage reliability. The gradual wear-out and process variation of NAND flash memory makes the worst-case oriented error correction code (ECC) in SSDs largely under-utilized most of the time. This work proposes to opportunistically leverage under-utilized error correction strength to allow error-prone flash memory I/O link over-clocking. Its rationale and key design issues are presented and studied in this paper, and its potential effectiveness has been verified through hardware experiments and system simulations. Using sub-22nm NAND flash memory chips with I/O specs of 166MBps, we carried out extensive experiments and show that the proposed design strategy can enable SSDs safely operate with error-prone I/O link running at 275MBps. Trace-driven SSD simulations over a variety of workload traces show the system read response time can be reduced by over 20%.