Enhancing Flash Memory Reliability by Jointly Considering Write-back Pattern and Block Endurance

Owing to high cell density caused by the advanced manufacturing process, the reliability of flash drives turns out to be rather challenging in flash system designs. To enhance the reliability of flash drives, error-correcting code (ECC) has been widely utilized in flash drives to correct error bits during programming/reading data to/from flash drives. Although ECC can effectively enhance the reliability of flash drives by correcting error bits, the capability of ECC would degrade while the program/erase (P/E) cycles of flash blocks is increased. Finally, ECC could not correct a flash page, because a flash page contains too many error bits. As a result, reducing error bits is an effective solution to further improve the reliability of flash drives when a specific ECC is adopted in the flash drive. This work focuses on how to reduce the probability of producing error bits in a flash page. Thus, we propose a pattern-aware write strategy for flash reliability enhancement. The proposed write strategy considers both the P/E cycle of blocks and the pattern of written data while a flash block is allocated to store the written data. Since the proposed write strategy allocates young blocks (respectively, old blocks) for hot data (respectively, cold data) and flips the bit pattern of the written data to the appropriate bit pattern, the proposed strategy can effectively improve the reliability of flash drives. The experimental results show that the proposed strategy can reduce the number of error pages by up to 50%, compared with the well-known DFTL solution. Moreover, the proposed strategy is orthogonal with all ECC mechanisms so that the reliability of the flash drives with ECC mechanisms can be further improved by the proposed strategy.