本文選題：UBIFS　切入點(diǎn)：NAND型閃存　出處：《南京大學(xué)》2013年碩士論文

【摘要】：閃存(Flash Memory)是一種常用于嵌入式系統(tǒng)的外存儲(chǔ)器,具有非易失、抗震蕩、低功耗、體積小等優(yōu)點(diǎn)。閃存主要包括兩種類型：NAND型和NOR型。近年來(lái),隨著NAND型閃存容量的快速增長(zhǎng),性價(jià)比的不斷提高,它比NOR型閃存更加廣泛地應(yīng)用于日常消費(fèi)電子產(chǎn)品中。閃存的普及不但取決于物理特性的優(yōu)劣,還取決于閃存文件系統(tǒng)的數(shù)據(jù)管理性能。傳統(tǒng)的閃存文件系統(tǒng)已經(jīng)不能滿足用戶在大容量NAND型閃存環(huán)境下對(duì)掛載速度、內(nèi)存消耗、讀寫(xiě)速度、磨損均衡等指標(biāo)的要求。作為新一代的閃存文件系統(tǒng),UBIFS是在Linux環(huán)境下實(shí)現(xiàn)的日志結(jié)構(gòu)文件系統(tǒng),解決了NAND型閃存作為MTD設(shè)備使用時(shí)遇到的若干技術(shù)瓶頸,具有廣泛的應(yīng)用前景。本文展開(kāi)了UBIFS的分析研究工作,并在快速掛載和熱數(shù)據(jù)識(shí)別方面設(shè)計(jì)了兩種優(yōu)化方案,改進(jìn)后的UBIFS達(dá)到了預(yù)定的優(yōu)化目標(biāo),具有一定的學(xué)術(shù)價(jià)值。目前有關(guān)UBIFS的中文分析文獻(xiàn)數(shù)量很少,對(duì)UBIFS文件系統(tǒng)的詳細(xì)分析就顯得有必要。本文概括介紹了UBIFS的系統(tǒng)結(jié)構(gòu),并且從UBI模塊和UBIFS模塊兩個(gè)角度出發(fā)對(duì)UBIFS的設(shè)計(jì)原理進(jìn)行了闡述,分析了映射管理、磨損均衡和文件索引等關(guān)鍵技術(shù)。針對(duì)分析過(guò)程中發(fā)現(xiàn)的問(wèn)題,本文分別在兩個(gè)層次上提出了優(yōu)化方案。在UBI模塊層,提出了一種以關(guān)機(jī)速度變慢為代價(jià)換取開(kāi)機(jī)速度提高的優(yōu)化方案。隨著閃存容量的不斷增大,掛載UBI模塊時(shí)掃描所有物理塊頭部信息的時(shí)間也不斷增加,導(dǎo)致嵌入式系統(tǒng)的啟動(dòng)變慢,這限制了UBIFS在大容量閃存領(lǐng)域的應(yīng)用前景。UBI模塊卸載時(shí)將物理塊的頭部信息集中保存到預(yù)留塊中,下次掛載時(shí)直接從預(yù)留塊中讀取頭部信息,這樣可以減少物理塊的掃描時(shí)間,從而加快開(kāi)機(jī)速度。測(cè)試結(jié)果表明,該優(yōu)化方案可以顯著提高UBI模塊的掛載速度。在UBIFS模塊層,寫(xiě)入數(shù)據(jù)被分為三種類型,不同類型的數(shù)據(jù)采用不同的物理塊分配策略。但是,這種數(shù)據(jù)分類方法是靜態(tài)的,無(wú)法動(dòng)態(tài)識(shí)別用戶數(shù)據(jù)中的熱數(shù)據(jù),從而影響了磨損均衡性能。通過(guò)借鑒內(nèi)存頁(yè)面置換算法,本文提出了兩級(jí)LRU(Least Recently Used)算法,并作為熱數(shù)據(jù)識(shí)別算法引入到UBIFS中,使數(shù)據(jù)的分類更加準(zhǔn)確。經(jīng)過(guò)實(shí)驗(yàn)驗(yàn)證,兩級(jí)LRU算法可以提高UBIFS文件系統(tǒng)的磨損均衡性能。
[Abstract]:Flash memory (Flash memory) is a kind of external memory commonly used in embedded system. It has the advantages of non-volatile, anti-shock, low power consumption and small volume. Flash memory mainly includes two types: NAND type and NOR type. In recent years, with the rapid growth of NAND flash memory capacity, With the increasing performance and price ratio, flash memory is more widely used in daily consumer electronics than NOR flash memory. The popularity of flash memory depends not only on physical properties, but also on physical properties. It also depends on the data management performance of flash file system. The traditional flash file system can no longer meet the user's load speed, memory consumption, read and write speed in large capacity NAND flash memory environment. As a new generation flash memory file system, UBIFS is a log structure file system implemented in Linux environment, which solves some technical bottlenecks when NAND flash memory is used as a MTD device. In this paper, the analysis and research work of UBIFS is carried out, and two optimization schemes are designed in terms of fast mount and thermal data recognition. The improved UBIFS achieves the target of optimization. It is necessary to analyze the UBIFS file system in detail. This paper introduces the system structure of UBIFS. The design principle of UBIFS is expounded from two aspects of UBI module and UBIFS module, and the key technologies such as mapping management, wear equalization and file index are analyzed. In the UBI module layer, an optimization scheme is proposed in exchange for the increase of startup speed at the cost of slower shutdown speed. With the increasing of flash memory capacity, the optimization scheme is proposed in this paper. The amount of time it takes to scan all physical block header information while mounting a UBI module is also increasing, resulting in slower startup of the embedded system. This limits the application prospects of UBIFS in the field of mass flash memory. When the UBI module unloads, the header information of the physical block is stored in the reserved block, and the header information is read directly from the reserved block on the next mount, which can reduce the scanning time of the physical block. The test results show that the optimized scheme can significantly improve the mount speed of UBI module. In the UBIFS module layer, the write data is divided into three types, and different types of data are allocated by different physical blocks. This data classification method is static and can not dynamically identify the thermal data in user data, thus affecting the performance of wear balance. By using the memory page replacement algorithm for reference, this paper proposes a two-level LRU(Least Recently used algorithm. As a thermal data recognition algorithm, it is introduced into UBIFS to make the classification of data more accurate. Experimental results show that the two-level LRU algorithm can improve the wear equalization performance of UBIFS file system.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2013
【分類號(hào)】：TP333

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