本文關(guān)鍵詞：層次混合存儲系統(tǒng)中緩存和預(yù)取技術(shù)研究　出處：《華中科技大學(xué)》2013年博士論文　論文類型：學(xué)位論文

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【摘要】：隨著固態(tài)盤(Solid State Disk, SSD)的普及,基于SSD和HDD (Hard Disk Drive)的混合存儲系統(tǒng)成為研究熱點�；旌洗鎯ο到y(tǒng)綜合了SSD的高IOPS、低延時和HDD的大容量、低成本的優(yōu)點。目前混合存儲系統(tǒng)有三類主要的組織方式：(1)SSD作為讀緩存和寫緩沖區(qū)來加速磁盤I/O；(2)磁盤作為寫緩沖區(qū)來減少SSD寫入；(3)SSD和磁盤均作為永久存儲,通過數(shù)據(jù)遷移和重映射來優(yōu)化系統(tǒng)性能。其中,方式(1)只需在原有磁盤存儲系統(tǒng)之上放置少量SSD充當(dāng)Cache便可大幅提高系統(tǒng)IOPS,具有低成本、易部署的優(yōu)勢,應(yīng)用最為廣泛。 SSD具有寫擦(Program/Erase, P/E)次數(shù)受限的特點,從而限制其在磁盤緩存上的應(yīng)用,同時其內(nèi)部繁重的垃圾回收任務(wù)會增加I/O的存取時延。此外,SSD作為Cache時,其大容量的特征會在很大程度上破壞底層存儲系統(tǒng)的訪問局部性,影響到底層存儲設(shè)備的I/O性能。針對SSD Cache帶來的壽命、性能和局部性弱化問題,通過緩存(Caching)和預(yù)取(Prefetching)技術(shù)以優(yōu)化由SSD和HDD構(gòu)成的混合存儲系統(tǒng)已成為工業(yè)界和學(xué)術(shù)界的重要課題。 首先,提出了一種基于SSD緩存(Flash Cache)和RAID的層次型混合存儲架構(gòu)RAF (Random Access First),該架構(gòu)引入適用于Flash Cache的成本收益模型,并支持隨機(jī)數(shù)據(jù)優(yōu)先的選擇性Cache插入策略。RAF將負(fù)載中順序訪問數(shù)據(jù)交給磁盤層,SSD僅需緩存那些具有高收益的隨機(jī)數(shù)據(jù),從而延長SSD的壽命并縮短系統(tǒng)響應(yīng)時間。此外,RAF通過將SSD緩存劃分為讀、寫區(qū)域,使得閃存層無效頁的分布更加集中,從而有利于回收塊的選取。實驗結(jié)果表明,與采用相同硬件配置的FlashCache相比,其平均響應(yīng)時間縮短了17%,磨損減少了53%。 其次,主存、SSD緩存以及磁盤構(gòu)成了多級緩存結(jié)構(gòu),針對當(dāng)前多級緩存結(jié)構(gòu)中SSD Cache受冷數(shù)據(jù)污染的問題,提出了一種基于層間訪問特征的旁路緩存算法CHPA (Characteristics between Hierarchies byPassing cache Algorithm)。CHPA是一種用于降低SSD寫開銷而設(shè)計的非同步多級緩存算法,通過數(shù)據(jù)塊在DRAM Cache內(nèi)和不同層間的訪問特征來預(yù)測熱數(shù)據(jù)塊,當(dāng)數(shù)據(jù)塊被上層DRAM Cache淘汰時,熱數(shù)據(jù)塊會被插入SSD緩存,而冷數(shù)據(jù)會繞過SSD層以減少寫入開銷。 再次,提出了一種基于SSD的順序預(yù)取策略FLAP (FLash-Aware Pre fetching)。 FLAP是一種具有高精確度的激進(jìn)式預(yù)取策略,通過基于關(guān)系圖的量化分析模型,并借助于SSD緩存容量大的優(yōu)勢,在Cache缺失時對磁盤設(shè)備進(jìn)行高精度、大長度預(yù)取,以節(jié)約預(yù)取成本。此外,通過從SSD空間中專門劃分出預(yù)取區(qū)域來存儲預(yù)取數(shù)據(jù),并采用時間相關(guān)的數(shù)據(jù)布局策略,FLAP使預(yù)取區(qū)域的垃圾回收效率大幅優(yōu)化,從而將預(yù)取操作對SSD壽命的影響降低到最小。 最后,由于DRAM和SSD組成的兩層緩存已經(jīng)過濾了大部分具有強(qiáng)時間局部性的數(shù)據(jù)訪問,因而在底層磁盤系統(tǒng)(如RAID系統(tǒng))中順序預(yù)取的作用變的更為重要。為此,提出了一種于面向分條的順序流預(yù)取算法SoAP (Strip-oriented Asynchronous Prefetching)。 SoAP是一種專門為并行磁盤系統(tǒng)設(shè)計的預(yù)取策略,通過將預(yù)取請求與分條(Strip)邊界對齊,并拆分為基于分條的子請求,來解決順序性缺失(Sequentiality Loss)等問題。此外,借助多隊列機(jī)制和異步調(diào)度策略,SoAP利用磁盤空閑帶寬來執(zhí)行預(yù)取操作,從而降低了預(yù)取開銷。
[Abstract]:With the solid state disk (Solid State Disk, SSD) SSD and HDD based on the popularity of (Hard Disk Drive) hybrid storage system has become a research hotspot. The hybrid storage system combines high IOPS SSD and HDD, large capacity and low delay, low cost. There are three main types of organization of mixed storage system: (1) SSD as read and write buffer cache to speed up disk I/O; (2) as disk write buffer to reduce the SSD writing; (3) SSD and disk as a permanent storage, through data migration and re mapping to optimize the performance of the system. Among them, the way (1) only needs to be put in a small amount of SSD on the original disk storage system as Cache can significantly improve system IOPS, has the advantages of low cost, easy deployment, the most widely used.
SSD has written (Program/Erase, P/E) cleaning the limited number of features, which limits its application in the disk cache on the garbage collection tasks at the same time the internal heavy will increase the access delay of I/O. In addition, as SSD Cache, the local access characteristics of the large capacity will destroy the underlying storage system to a great extent the performance of I/O bottom layer storage device. For SSD Cache brings the problem of life, weakening performance and locality, caching and prefetching (Caching) (Prefetching) hybrid technology to optimize the storage system composed of SSD and HDD has become an important topic in academia and industry.
First, we propose a SSD based cache (Flash Cache) hierarchical hybrid storage architecture and RAID RAF (Random Access First), the cost income model is introduced into this architecture for Flash Cache, and support the selective Cache random data priority insertion strategy.RAF will load in order to access the data to disk, only SSD to cache random data those with high income, so as to extend the life span of SSD and shorten the response time of the system. In addition, RAF SSD will write through cache area divided into reading, the distribution of flash layer invalid page more centralized, and is conducive to the recovery from the block selection. The experimental results show that, compared with the same hardware configuration FlashCache, the average response time is shortened by 17%, the wear is reduced by 53%.
Second, memory, and disk cache SSD constitute a multi-level cache structure, in view of the current structure of SSD Cache in a multi-level cache by the cold data pollution problem, proposes a bypass cache algorithm CHPA layer access feature based (Characteristics between Hierarchies byPassing cache Algorithm.CHPA) is designed for reducing overhead and non SSD synchronous multi cache algorithm, prediction data block through the data blocks in the DRAM and Cache in different layers of access to features, when the data block is eliminated when the upper DRAM Cache, data block will be inserted into the SSD cache, and cold data will bypass the SSD layer to reduce the write overhead.
Again, put forward a strategy based on the FLAP sequence of pre SSD (FLash-Aware Pre fetching). FLAP is a radical pre fetching strategy with high accuracy, by analyzing the quantitative relationship model based on the graph, and with the help of the advantages of SSD cache capacity, high precision of the disk device in the absence of Cache. Large length prefetching, in order to save the cost of prefetching. In addition, the SSD space from a specialized division of the prefetch area to store prefetched data, and the data layout strategy of the time, the FLAP prefetching region significantly optimize the efficiency of garbage collection, which will prefetch operation influence on the life of SSD is reduced to the minimum.
Finally, because of the two layers of DRAM and SSD is composed of cache filter most strong temporal locality of data access, and at the bottom of the disk system (such as RAID) in order to prefetch the effects become more important. Therefore, put forward a kind of oriented strip sequence prefetching algorithm (SoAP Strip-oriented Asynchronous Prefetching). SoAP is dedicated to a parallel disk system design Prefetching Strategy, the prefetch request and the boundary alignment (Strip), and split into sub sub requests based on order to solve the lack of (Sequentiality Loss) and other issues. In addition, with the help of multi queue and asynchronous mechanism scheduling strategy, using SoAP disk idle bandwidth to perform prefetch operation, thereby reducing the prefetch overhead.

【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2013
【分類號】：TP333

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相關(guān)期刊論文 前1條

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本文編號：1412843