固态硬盘的闪存转换层映射策略研究

发布时间：2018-01-03 12:38

本文关键词：固态硬盘的闪存转换层映射策略研究　出处：《重庆大学》2012年硕士论文　论文类型：学位论文

【摘要】：固态硬盘因其读写速度快、低功耗、无噪音、抗震动、低热量、体积小和非易失等特点而被广泛应用于军事、车载、视频监控、网络监控、网络终端、电力、航空等领域。但是由于固态硬盘的物理结构和存储介质NAND FLASH的先擦后写以及擦除次数有限等特性使得应用于传统硬盘的文件系统不能直接应用于固态硬盘。解决这些问题的方案是在闪存设备之上增加一个FTL(Flash TranslationLayer)将闪存设备模拟成与磁盘一致的块设备结构，从而使得传统的存储管理技术可以直接应用于闪存设备上。 FTL在闪存管理上有着重要的作用，近些年来，三种类型的FTL算法被相继提出，分别是页映射，块映射和混合映射。页映射可以把任意一个逻辑页映射到任意的物理页，高效灵活但是映射表会消耗很多SRAM。块映射只有逻辑块和物理块可以任意映射，每个页只能映射到某个物理块中固定位置，节省了很多SRAM但是减少了很多页的映射机会，会导致垃圾回收频繁运行，，影响整个系统性能。混合映射是把一小部分最近更新过的页使用页映射，余下的页使用块映射，但是这个方法在垃圾回收的时候，逻辑很复杂，需要各种合并操作，性能也容易差。现在主流的做法是把最近使用过的映射表作为热数据，缓存在有限的SRAM里，然后把大部分的映射表放在闪存上，依靠局部性来加速映射速度，提高IOPS。本文的研究工作主要包括以下几个方面： ①研究了固态硬盘的关键技术，SAS接口技术，多通道并行技术，这两项技术是固态硬盘性能提升的关键。深入研究了固态存储的垃圾回收原理和磨损均衡策略。 ②研究了闪存转换层的必要性及其基本原理；研究了目前常用和主流的FTL算法，分析了相关技术问题以及解决方案，并用Flashsim仿真模拟器对相关算法进行了对比仿真。 ③设计了一种闪存转换层映射策略。本文深入研究DFTL算法，从DFTL策略实现技术分析入手，指出了其所存在的局限性，提出了改进后的ADFTL算法，同时考虑了数据访问的时间和空间局部性，从而有效的提高了缓存的命中率，减少了垃圾回收负荷，加快了系统响应，减少了块的擦除次数。用Flashsim仿真模拟器仿真的结果证明了所设计的闪存转换层映射策略的有效性。
[Abstract]:Solid state hard disk is widely used in military, vehicle-borne, video surveillance, network monitoring, network terminal and electric power because of its high speed of reading and writing, low power consumption, noise free, aseismic, low heat, small volume and non-volatile. But due to the physical structure of solid state hard disk and storage medium NAND. The characteristics of FLASH, such as first erasing and then writing and limited erasing times, make the file system applied to traditional hard disk can not be directly applied to solid state disk. The solution to these problems is to add an FT to the flash memory device. L(. Flash Translation layer simulates the flash device into a block device structure consistent with the disk. Thus, the traditional storage management technology can be directly applied to flash memory devices. FTL plays an important role in flash memory management. In recent years, three types of FTL algorithms have been proposed one after another, namely page mapping. Block mapping and hybrid mapping. Page mapping can map any logical page to any physical page. It is efficient and flexible but the mapping table will consume a lot of SRAM.Block mapping only logical and physical blocks can be mapped arbitrarily. Each page can only be mapped to a fixed location in a physical block, saving a lot of SRAM but reducing mapping opportunities for many pages, resulting in garbage collection running frequently. Hybrid mapping uses page mappings for a small number of recently updated pages and blocks for the rest, but this approach is complex when garbage collection occurs. It requires a variety of merge operations and performance is easy. The prevailing practice now is to use the recently used mapping table as hot data, cache it in a limited SRAM, and then place most of the mapping tables on flash memory. Rely on locality to accelerate mapping speed and improve IOPS. The research work of this paper mainly includes the following aspects: 1. The key technology of solid state hard disk, SAS interface technology and multi-channel parallel technology are studied. These two technologies are the key to improve the performance of solid-state hard disk. The principle of solid state storage garbage collection and wear equalization strategy are deeply studied. (2) the necessity and basic principle of flash memory conversion layer are studied. In this paper, the common and mainstream FTL algorithms are studied, and the related technical problems and solutions are analyzed, and the relative algorithms are compared and simulated with the Flashsim simulation simulator. 3. This paper designs a mapping strategy of flash memory conversion layer. This paper deeply studies the DFTL algorithm, and points out its limitations from the technical analysis of DFTL strategy implementation. An improved ADFTL algorithm is proposed, which considers the time and space localization of data access, which improves the hit rate of cache effectively, reduces the garbage collection load, and speeds up the system response. The simulation results of Flashsim simulator show the effectiveness of the proposed mapping strategy.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TP333.35

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