Access Characteristic Guided Read and Write Regulation on Flash Based Storage Systems

NAND flash memory is now used in various storage systems, such as embedded systems, personal computers, and web servers. The developments in bit density and technology scaling have reduced its price, but worsen the reliability, leading to shortened lifetime and degraded access performance. This paper proposes to exploit access characteristics of workloads to improve flash performance and lifetime. The basic idea is to regulate the read and write operations based on the identified access characteristics. First, an access cost model is presented, which indicates a tradeoff between read and write time cost on NAND flash memory. Based on the access characteristics of workloads, read-only pages will be written with high cost so that they can be read with low cost, and write-only pages will be written with low cost. Second, the tradeoff between read cost and flash wearing is exploited for lifetime improvement. The write requests on write-only data are processed with reduced wearing by regulating the program threshold voltage. Finally, as these approaches apply different write operations on write-only data for performance and lifetime improvement respectively, a combined approach is proposed to satisfy both goals. Simulation results show that the proposed approaches can improve performance and lifetime significantly with negligible overhead.