HaWL: Hidden Cold Block-Aware Wear Leveling Using Bit-Set Threshold for NAND Flash Memory

Abstract

In this letter, we propose a novel wear leveling technique we call Hidden cold block-aware Wear Leveling (HaWL) using a bit-set threshold. HaWL prolongs the lifetime of flash memory devices by using a bit array table in wear leveling. The bit array table saves the histories of block erasures for a period and distinguishes cold blocks from all blocks. In addition, HaWL can reduce the size of the bit array table by using a one-tomany mode, where one bit is related to many blocks. Moreover, to prevent degradation of wear leveling in the one-to-many mode, HaWL uses bit-set threshold (BST) and increases the accuracy of the cold block information. The performance results illustrate that HaWL prolongs the lifetime of flash memory by up to 48% compared with previous wear leveling techniques in our experiments.

RRWL: Round Robin-Based Wear Leveling Using Block Erase Table for Flash Memory

“…In our experiments, we compare the performance of RRWL with BET and HaWL [2], [3]. Table 1 shows details of experiment parameters used.…”

“…However, these information tables require additional memory space and they have to be minimized in limited memory space requirements. Therefore, to reduce the memory consumption of information tables, block erase table (BET) techniques have been studied [2], [3].…”

“…However, a conventional BET technique has a hidden cold block problem. The hidden cold block problem is a phenomenon that information of cold blocks disappears with the erase operation of hot blocks in one-to-many mode [3]. The performance of wear leveling is degraded by the hidden cold block problem in one-to-many mode of BET.…”

“…The performance of wear leveling is degraded by the hidden cold block problem in one-to-many mode of BET. To solve the hidden cold block problem, HaWL uses a bit-set threshold, which is based on a maximum deviation compared with the average invalid page count of blocks related to each bit in BET [3]. However, identifying cold blocks based on the number of invalid pages has limitations in particular cases.…”