描述
TC-PCIC02
RAID級(jí)別可以相互組合或通過(guò)擴(kuò)展,形成諸如RAID10、50和60等RAID級(jí)別。人們往往對(duì)這種擴(kuò)展的RAID級(jí)別不甚了解。不過(guò),這些復(fù)雜的RAID級(jí)別添加了一些極其有趣的特性,比方說(shuō):R1E(2個(gè)以上磁盤(pán)或奇數(shù)磁盤(pán)的鏡像)R5E(與R5一樣,但支持“熱”備用磁盤(pán)容量)R5EE(與R5E一樣,但每個(gè)條帶都支持“熱”備用磁盤(pán))
需要進(jìn)一步考慮的是RAID10、50和60等復(fù)雜的RAID級(jí)別,它們提供了一些非常有趣的未知特性。它們基本上能提供相同級(jí)別、和尺寸的RAID卷組合,此外采用RAID0方式在他們之間分配條帶化數(shù)據(jù),以此平衡性能。比方說(shuō),20個(gè)驅(qū)動(dòng)器組成的RAID50,可分成4個(gè)RAID5陣列,每個(gè)陣列有5個(gè)磁盤(pán),然后這四個(gè)RAID5陣列之間采用RAID0方式配置條帶化數(shù)據(jù)。不過(guò),問(wèn)題在于,為什么要選擇20個(gè)磁盤(pán)組成RAID50這種復(fù)雜的RAID級(jí)別,而不用20個(gè)同樣的磁盤(pán)組成簡(jiǎn)單的RAID5呢?
主要原因在于,如果我們看看RAID5的讀取性能就會(huì)發(fā)現(xiàn),在降級(jí)模式時(shí)其讀取性能非常差。為了從壞塊/死盤(pán)恢復(fù)數(shù)據(jù),必須讀取19個(gè)沒(méi)問(wèn)題的磁盤(pán),并對(duì)每個(gè)磁盤(pán)進(jìn)行18次XOR運(yùn)算,而后才能返回?cái)?shù)據(jù)。也就是說(shuō),這時(shí)的讀取速度僅為正常讀取速度的二十分之一,而且涉及的磁盤(pán)越多,讀取性能就變得更糟。同樣,重構(gòu)也非常復(fù)雜。假設(shè)每個(gè)磁盤(pán)為1TB,如果重構(gòu)的話,那么就需要移動(dòng)20TB的數(shù)據(jù),XOR為19TB(這可能需要數(shù)周才能完成)。
可編程控制器是70年代以來(lái),計(jì)算機(jī)迅速發(fā)展在工業(yè)控制領(lǐng)域?qū)樞蚩刂朴兄卮笠饬x的一種新興技術(shù),由于它編程直接,方便,抗干擾能力強(qiáng),工業(yè)控制中幾乎所有的順序控制都可簡(jiǎn)單地由它完成,因而其應(yīng)用愈來(lái)愈廣泛。電動(dòng)行車是現(xiàn)代化生產(chǎn)中用于物料輸送的重要設(shè)備,傳統(tǒng)的控制方式下,大都采用人工操縱的半自動(dòng)控制方式,在許多場(chǎng)合,為了提高工作效率,促進(jìn)生產(chǎn)自動(dòng)化和減輕勞動(dòng)強(qiáng)度,往往需要實(shí)現(xiàn)電動(dòng)行車的自動(dòng)化控制,實(shí)現(xiàn)自動(dòng)化控制,可以使行車能夠按照預(yù)定順序和控制要求,自動(dòng)完成一系列的工作。本文介紹了工廠電鍍車間的電鍍專用行車,利用PLC構(gòu)成一套自動(dòng)控制系統(tǒng),實(shí)現(xiàn)對(duì)電鍍專用行車的自動(dòng)控制過(guò)程。
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