為了更清晰的認(rèn)識(shí)我們所生存的環(huán)境，提高人際溝通效率，人們收集和創(chuàng)造了大量的數(shù)據(jù)，有些是對(duì)物理世界的客觀描述，如原子和分子的組成，或是DNA螺旋結(jié)構(gòu)；也包括煙波浩渺的宇宙中的星系和星云；亦或是人類(lèi)對(duì)自身歷史的記錄；還有一些數(shù)據(jù)被用于人們相互溝通，如Facebook上每天新增數(shù)十億條內(nèi)容，或每天被發(fā)送的數(shù)千億封郵件。

    隨著人們對(duì)客觀世界的逐步認(rèn)知，人際溝通的效率越來(lái)越高，人們的溝通與生活也越來(lái)越豐富，人類(lèi)收集和創(chuàng)造的數(shù)據(jù)也越來(lái)越多，這些數(shù)據(jù)飽含信息與知識(shí)，是人類(lèi)智慧與勤勞的結(jié)晶，是人類(lèi)寶貴的信息資產(chǎn)。一部《史記》，共52萬(wàn)6千500字，約1MB數(shù)據(jù)；一組用于基因研究的染色體照片數(shù)據(jù)量超過(guò)2TB；歐洲核子研究中心(CERN)每年有超過(guò)20PB數(shù)據(jù)通過(guò)全球最大的大型強(qiáng)子對(duì)撞機(jī)(LHC)被收集起來(lái)用于微觀粒子研究。根據(jù)IDC的分析，2011年全球數(shù)據(jù)產(chǎn)生量達(dá)到1.8ZB，到2020年這個(gè)數(shù)字將增長(zhǎng)50倍（1ZB=1,000EB=1,000,000PB），如此大規(guī)模的數(shù)據(jù)給存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" title="存儲(chǔ)">存儲(chǔ)" 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    存儲(chǔ)方案的演進(jìn)

    在人類(lèi)發(fā)明和使用電子計(jì)算機(jī)以前，數(shù)據(jù)處理由人類(lèi)大腦完成，大腦中還同時(shí)存儲(chǔ)了大量信息用于支撐數(shù)據(jù)處理，人類(lèi)大腦存儲(chǔ)的信息依然相對(duì)有限，仍有大量數(shù)據(jù)被存儲(chǔ)在圖書(shū)館。當(dāng)有需要的時(shí)候，人們便會(huì)到圖書(shū)館獲取更多的數(shù)據(jù)。以此我們可以總結(jié)出如下的一種數(shù)據(jù)存儲(chǔ)與數(shù)據(jù)處理模型：

    該模型包括三個(gè)部分，計(jì)算單元、內(nèi)部存儲(chǔ)單元（低延遲，容量偏?。?、外部存儲(chǔ)單元（延遲增加，容量超大）。如果按照對(duì)圖書(shū)的存儲(chǔ)(記憶)能力來(lái)估算，通常一個(gè)人大腦中能記憶的內(nèi)容不超過(guò)1000本書(shū)，圖書(shū)館中收藏的書(shū)籍大約是百萬(wàn)本為單位。兩種存儲(chǔ)的存儲(chǔ)容量差距大概是1000倍，而且圖書(shū)館中的數(shù)據(jù)可以被很多人共享。

    20世紀(jì)電子與信息技術(shù)迅速發(fā)展，機(jī)器計(jì)算迅速普及，馮·諾依曼在1945年6月30日，提出了存儲(chǔ)程序邏輯架構(gòu)，即現(xiàn)有的計(jì)算機(jī)都遵循的“馮·諾依曼體系架構(gòu)”，具體如下圖：

    我們可以看出，馮諾依曼體系結(jié)構(gòu)與人腦（生物）計(jì)算模型匹配度相當(dāng)準(zhǔn)確。我們通常把運(yùn)算器和控制器合并成中央處理器（CPU），內(nèi)部小容量的存儲(chǔ)提供快速的訪問(wèn)，外部存儲(chǔ)器提供大容量的存儲(chǔ)空間。在不同的計(jì)算機(jī)時(shí)代，我們可以按照不同的角度來(lái)理解馮諾依曼體系結(jié)構(gòu)。在單機(jī)計(jì)算時(shí)代（包括大型機(jī)、小型機(jī)、微機(jī)）內(nèi)部存儲(chǔ)器可理解為內(nèi)存（即Memory），外部存儲(chǔ)器可理解為物理硬盤(pán)（包括本地硬盤(pán)和通過(guò)網(wǎng)絡(luò)映射的邏輯卷）。在本地硬盤(pán)空間不足，可靠性無(wú)法滿(mǎn)足業(yè)務(wù)需求的情況下，SAN存儲(chǔ)出現(xiàn)了，通過(guò)網(wǎng)絡(luò)映射的邏輯卷（即SAN存儲(chǔ)提供的LUN）成為增強(qiáng)版的硬盤(pán)。為了解決數(shù)據(jù)共享的問(wèn)題，NAS存儲(chǔ)隨之誕生。

    但馮諾依曼體系架構(gòu)沒(méi)有考慮并行計(jì)算和數(shù)據(jù)共享情形，在如今的網(wǎng)絡(luò)時(shí)代，大量計(jì)算設(shè)備通過(guò)網(wǎng)絡(luò)形成一個(gè)龐大、相互獨(dú)立但又邏輯統(tǒng)一的計(jì)算系統(tǒng)，因此我們可以總結(jié)出一個(gè)數(shù)據(jù)存儲(chǔ)的通用模型，這個(gè)模型包括兩級(jí)存儲(chǔ)，其存儲(chǔ)容量差距約1000倍：

    如果將上圖中每一個(gè)計(jì)算模塊理解為一個(gè)計(jì)算內(nèi)核，那么高速存儲(chǔ)單元?jiǎng)t是CPU內(nèi)的緩存（單位為KB~MB），海量存儲(chǔ)單元?jiǎng)t是內(nèi)存（單位為GB）；如果把每一個(gè)計(jì)算模塊理解為一個(gè)CPU，那么高速存儲(chǔ)單元?jiǎng)t是內(nèi)存（單位為GB~TB），海量存儲(chǔ)是物理硬盤(pán)或通過(guò)網(wǎng)絡(luò)映射給服務(wù)器的邏輯卷（或網(wǎng)絡(luò)文件系統(tǒng)，單位為T(mén)B~PB）；如果把計(jì)算模塊理解為針對(duì)某一項(xiàng)任務(wù)或某一組任務(wù)提供計(jì)算能力的服務(wù)器集群，把SAN或NAS等擁有TB~PB級(jí)存儲(chǔ)規(guī)模的網(wǎng)絡(luò)存儲(chǔ)設(shè)備理解為高速存儲(chǔ)單元，那么具備PB~EB級(jí)存儲(chǔ)容量的海量存儲(chǔ)單元將基于什么技術(shù)和產(chǎn)品構(gòu)建呢？

     SAN和NAS技術(shù)已經(jīng)出現(xiàn)了數(shù)十年，目前單臺(tái)SAN或NAS設(shè)備最大容量已經(jīng)達(dá)到PB級(jí)別，但在應(yīng)對(duì)EB級(jí)數(shù)據(jù)挑戰(zhàn)時(shí)，還是顯得有些力不從心。這主要由于其架構(gòu)和服務(wù)接口決定的。

    SAN使用SCSI協(xié)議作為底層協(xié)議，SCSI協(xié)議管理的粒度非常小，通常以字節(jié)(byte)或千字節(jié)(KB)為單位；同時(shí)SCSI協(xié)議沒(méi)有提供讀寫(xiě)鎖機(jī)制以確保不同應(yīng)用并發(fā)讀寫(xiě)時(shí)的數(shù)據(jù)一致性，因此難以實(shí)現(xiàn)EB級(jí)存儲(chǔ)資源管理和多個(gè)服務(wù)器/服務(wù)器集群之間數(shù)據(jù)共享。