| Along with science and technology unceasing progress, people request thestorage device more and more. According to the law of mole, the capacity ofturbine wheel mechanical hard disk which we usually use to growing quickly,the speed also unceasing enhanced. The interface technology also improved, newgeneration of Enhanced IDE (Strength IDE)'s highest transmission speed mayreach as high as the 150MB/second (Ultra ATA/150).As soon as talks about the data of reliability, stability, the mechanical harddisk paled by comparison. The data not only has no high guarantee in thesecurity, on the machinery anti-knocking property, anti-shocked also is unable tolet people to accept. Regarding to temperature compatible is not also extremelysatisfaction. It is unable to satisfy under the extreme condition work. Speaks ofthe power, the turbine wheels revolved at high speed of 7200 round/min,increase the power, also increase the calorific power, also make the machineryaging intensify at the same time.If considering to individual PC application only, regarding to the memorycontent's completion request is not demand high, the mechanical hard disk is theextremely ideal storage medium. But along with the communicationdevelopment, in-bedded system's progressing, the hard disk applies not merelyin the computer, used widespread in large-scale communication facility, just likeswitch, gateway, 3G service networks and so on. In order to provides peopleinformation services of continuously , reliable, these equipment works alongthe year round and cannot be turned off , Regarding to this kind of ultra longtime work continuously, the mechanical hard disk is unable to guarantee thenormal work.The IBM expert once suggested that we should not have to let the hard diskoperating surpass for 10 hours in one day, do not let the hard disk working for 8hours continuously. Otherwise will reduce the mechanical hard disk's life greatly.The mechanical hard disk is easy to have the physical damage;moreoverread-write frequently will cause the hard disk products "the fragment", seriouslyinfluence access speed. Therefore in correspondence domain, hard disk damagerate, failure rate are extremely high, regarding to the product performance andMTBF (average does not have fault time), have a great affectation. Moreoverproduce the extra maintenance cost and product believing influence.In view of the mechanical hard disk stability is bad, unable to apply in thecorrespondence domain effectively. We considered using a kind of stable andreliable storage medium to substitutes. The solid state hard disk is the FLASHhard disk (is also been called electronic disk). The solid state hard disk applies inthe military, the aerospace and the special domain early. Along with the FLASHcraft in improvement, the cost reduces year by year, multistage unit memorytechnology (MLC multi-level cell, unit two bits) progressing, the price reduces,the solid state hard disk changes civilly gradually. Especially in thecorrespondence domain, the ZTE, HUAWEI, UT-starcom and the well-knowndomestic enterprise already started to apply.In the ordinary circumstances, the hard disk is not surpass 10G in thecorrespondence domain, the mechanical hard disk is wastes in the capacity evenif uses 80G, when the reliability and the cost achieved balances, the solid statehard disk is a good choice.The solid state hard disk does not have the mechanical magnetic head, sohas no sought time, saves on the mechanical hard disk from the non-volatilityhas not distinguished. The reliability, the anti-knocking are high, retain the dataafter power off, may provide 1 million MTTF. An interface of in-beddedsubstitute mechanical hard disk, seamlessly.Although the solid state hard disk has many advantages, but has manymalpractices. The solid state hard disk is based on the FLASH technology,FLASH has the slightly capacity itself, low access speed, the number of writetimes limitedly, the smallest eraser unit is "the block", erase the same placecontinuously is easy to wear out , becomes read-only. In order to overcome theseshortcomings, the solid state hard disk usually use advanced method to make upthese flaws. At present the development of solid state hard disk company is notmore in the world, The leaders are M-system, Samsung Corporation and so on.M-system proposed a main technology is TrueFFS (True Flash File System),including Wear -leveling, Garbage Collection (fragment recycling), dataconnection, Bad-Block Mapping, ECC/EDC (Reed-solomon) algorithm and soon. These algorithm make up the shortcoming of FLASH chip, manifests thesuperiority of solid state hard disk. From above we can see that solid state harddisk is not only the FLASH chip which piecing together simply, but also trulyhard disk.At present, the solid state hard disk is being at the development phase, alsoneeds to improve. Mainly manifests in:1) The hard disk capacity is low. Be suitable only for the special use, cannottrue replace the turbine wheel hard disk, especially facing the 3G time arrival,the storage space which Video NET will need is inestimable.2) The low access speed: Although many companies already promoted thehigh speed solid state hard disk (the speed: Reads 57MB/S, writes 37MB/S) now,but its improvement factor is based on to the FLASH chip improvement, is haslow performance to price.3) Hardware architecture obsolete: At present the solid state hard disk is notideal in the field regarding to the FLASH array structure optimization, majorityof uses is old style of TDM, and the main reason is the spatial limitation and thehigh density layout.4) algorithm improvement: ECC/EDC, wear leveling , the fragmentrecycling, the data association, address mapping algorithm have no standard,M-system TrueFFS which is mature already in the Voxworks, but is only use topartial chips, to a new chip, we have to coding a new driver, certainly theTrueFFS is a key point which we profits from.From above, the solid state hard disk has more advantage. But because ofprevented in space, in price, in interface standard limit. The present solid statehard disk used only for facilitate, the general IDE interface. But the true flawalso lies in the capacity is low, usually 1G used on the single board, may use inmerely the main software. Regarding to complete such as the video servicedemand is by far insufficient. Moreover, as high as 500 US dollars pricesenhanced the overall system cost imperceptibly, regarding to amount of spaceused system, and cost is in a barrier.This article proposed one kind of "applies in the correspondence domainbased on TrueFFS theoretical" design of FLASH memory array, uses inovercoming the solid state hard disk in the correspondence domain use barrier.The important attribute to realize lies in spatial. The memory array may bybuckle the board, no longer rigidly adheres to 3.5 inches, 2.5 inches physicalspaces, but in the relative area the storage capacity increases, and by the flexiblehardware architecture, optimized the TrueFFS algorithm, enhances the memorysystem's reliability and speed. Its function realized as the hard disk function,therefore we still call it solid state hard disk. |
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