摘要
在采用SLC(Single-Level-Cell)和MLC(Multi-Level-Cell)闪存的混合固态硬盘设计中,SLC和MLC之间的写数据分配和磨损均衡是混合固态硬盘闪存转换层设计的关键问题之一.针对此问题,提出一种具有磨损均衡意识的混合固态硬盘闪存转换层算法——WLAFTL(Wear Leveling Aware Flash Translation Layer).首先,它提出了一种动态的基于磨损均衡思想和请求大小融合的数据分配机制,即根据SLC和MLC的磨损速率来动态调整热数据识别阈值的大小,然后将小的写请求分配到SLC、大的写请求分配到MLC.其次,它提出了一种基于磨损均衡思想与数据先进先出(FIFO)调度策略融合的SLC冷数据回收/迁移机制,减少由SLC向MLC迁移的数据量.实验结果显示,与ComboFTL和CFTL算法相比,在使用相同地址映射机制的条件下,WLAFTL算法的平均响应时间分别平均有13.6%和12.7%的改善,总的擦除次数分别平均减少9.2%和20.4%,同时能够更好地实现SLC和MLC之间的磨损均衡.
With the rapid development of NAND flash memory technologies,replacing hard disks with NAND flash based solid state disks(SSDs)has become a recently emerging trend in computer storage domain.Nowadays,SSDs are mainly based on homogeneous NAND flash chips such as single-level cell(SLC)flash chips and multi-level cell(MLC)flash chips.SLC and MLC chips are distinctive in terms of capacity,performance,and endurance.Specifically,SLC has the advantage of fast read/write,low power consumption and long life,and MLC has the advantage of capacity units with low cost.Therefore,it is a promising method to design hybrid SSDs,consisting of both SLC and MLC flash chips,to achieve a response time and lifetime as same as a SLC-based SSD while maintaining the price of a MLC-based SSD.In order to realize these design goals of hybrid SSDs,the key issues are:(1)how to allocate data into SLC and MLC region;and(2)how to make wear leveling between SLC region and MLC region.In other words,SLC region should be used to store hot data(frequently accessed or updated data)to benefit from its fast read and write performance and long durability,and MLC region should be used to store cold data to benefit from its low cost and large capacity.Meanwhile,the SLC and MLC region should be synchronous wear as far as possible to realize the same lifespan of heterogeneous SLC/MLC chips.In order to solve these problems,this paper proposes a wear leveling aware flash translation layer(WLAFTL)for hybrid SSDs.Firstly,WLAFTL proposes a dynamic data allocation scheme,which is based on the fusion of wear leveling and write-request size.Specifically,it employs a traditional write-request size based hot or cold data identification and allocation scheme which identifies write requests whose size is less than the threshold value as hot data and sends them to SLC region,and identifies the rest of data as cold data and sends them to MLC region.However,the threshold value of hot or cold data identification is not fixed and can be adaptively adjusted according to the wear speed of SLC and MLC region.Secondly,WLAFTL proposes a garbage collection or migration scheme of cold data for SLC region,which is based on the fusion of wear leveling and first in first out(FIFO)strategy.Specifically,it employs FIFO strategy to manage the data block in SLC region,and when the space of SLC region is not enough,it employs the following scheme to make room for newly arrived hot data:if SLC region wears faster than MLC region,the valid data block of the first in SLC region is immediately migrated into MLC region;otherwise,the valid data block of the first in SLC region is collected into SLC region no more than N times.Our experiment results demonstrate that under the condition of using the same address mapping scheme,compared to ComboFTL and CFTL,WLAFTL can achieve up to 13.6%and 12.7%average response time improvement,as well as 9.2%and 20.4%total block erasure reduction,respectively.Moreover,it can achieve better wear leveling between SLC and MLC than ComboFTL and CFTL.
作者
姚英彪
王发宽
YAO Ying-Biao;WANG Fa-Kuan(School of Communication Engineering,Hangzhou Dianzi University,Hangzhou 310018;School of Telecommunication and Information Engineering,Nanjing University of Posts&Telecommunication,Nanjing 210003)
出处
《计算机学报》
EI
CSCD
北大核心
2018年第10期2379-2393,共15页
Chinese Journal of Computers
基金
国家自然科学基金项目(61100044
61671192)
浙江省重点科技创新团队项目(2013TD03)
"电子科学与技术"浙江省一流学科A类资助~~
作者简介
姚英彪,男,1976年生,博士,教授,中国计算机学会(CCF)会员,主要研究领域为存储系统设计、无线传感器网络、媒体信号处理等.E-mail:yaoyb@hdu.edu.cn.联系电话:13282105137.;王发宽,男,1991年生,硕士,工程师,主要研究方向为固态硬盘存储技术.E-mail:w469144949@163.com.
