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1、信息存储材料与技术第1页，本讲稿共29页第2页，本讲稿共29页光存储 v光存储最早的形式是缩微照相：文档资料长期保存的主要形式。将文献摄影，存放于缩微胶片上，缩微胶卷、缩微教胶片、缩微卡片等。v激光全息：实现三维图像存储不能进行实时数据存取。v光盘技术：光盘存储技术是本世纪70年代开拓出来的。光盘存储集成系统中，光盘机和光盘片是核心器件。在光盘机中光学读、写头是关键元件。第3页，本讲稿共29页 光盘存储器（简称光盘存储器（简称“光盘光盘”）是利用激光原理存储和读取信息的）是利用激光原理存储和读取信息的媒介。光盘片用塑料制成，塑料中间夹入了一层薄而平整的铝膜，通过媒介。光盘片用塑料制成，塑料中间
2、夹入了一层薄而平整的铝膜，通过铝膜上极细微的凹坑记录信息。铝膜上极细微的凹坑记录信息。只读光盘：只读光盘：信息是光盘制作时在盘面上一次性形成的，只能读出 使用，不能重新写入。工厂通过压制方法生产光盘时，将信息以凹坑形式生成在铝膜上，成为永久的信息记录。一片普通5”只读光盘可以存放650MB的信息。只读光盘是一种非常好的可以长期保存的存储介质，今天许多商品软件和信息资料都被制成光盘销售。刻录光盘：刻录光盘：数据一旦进入光盘，所占的空间是不能释放的。可读写光盘：可读写光盘：也已投放市场。光盘光盘的结构特点和工作原理的结构特点和工作原理第4页，本讲稿共29页光盘光盘和工作原理和工作原理光盘表面：光盘
3、表面：0/1光光盘盘外外观观光盘工作原理光盘工作原理激光束撞击光盘表面凹坑平面棱镜反射激光束激光二极管感光二极管聚焦光脉冲转换为0/1第5页，本讲稿共29页偶氮偶氮第6页，本讲稿共29页光存储基本原理光存储基本原理光烧孔光烧孔：光物理烧孔、光化学烧孔第7页，本讲稿共29页电子俘获电子俘获第8页，本讲稿共29页第9页，本讲稿共29页第10页，本讲稿共29页It is estimated that the human race has created about 1exabyte(1018)of information to date.It is also predictedthat the ne
4、xt exabyte could be generated within the next three years.This unprecedented growth in information poses a number of significant challenges in terms of information storage,transmission,networking,and access.Storage services are currently growing at 120 percent a Year and are directly linked to the g
5、rowth in geographically geographically dispersed online activities.第11页，本讲稿共29页Organizations are rapidly realizing that their central data storage facilities are called on by employees not only in the metropolitan area,but worldwide.Optical networks,however,have not been developedand optimized with
6、data storage in mind,although it isnow realized that they represent the main solution availabletoday for networking geographically dispersed storage and users.第12页，本讲稿共29页Fabric attached storage,which includes storage area networks(SANs)and network attached storage(NAS),represents one of the fastest
7、 growing areas ofnetworking.Its goals include providing timely access to information,large capacity,dynamic reconfigurable behavior,data protectionand restoration,as well as covering a large Geographic coverage.SANs can offer unique advantages,including consolidated storage with cost savings and rec
8、onfigurability,greater utility of centralized/distributed data,and data protection through replication for disaster recovery.This feature topic provides an overview of optical storage area networks.第13页，本讲稿共29页considers next-generation optical storage area networks based on the light-trails approach
9、 to dynamic wavelength provisioning.It discusses SAN extensions based on light-trails and pays attention to Disaster recovery and grid computing in the context of SANs.evaluates the reliability and availability of SAN extension solutions including IPbased extensions and Fibre Channel(FC)-based exten
10、sions.considers dispersion compensation for SANs where data centers still use legacy 第14页，本讲稿共29页multimode fiber with a limited bandwidth-distanceproduct.The article discusses the use of enhanced Bandwidth multimode fiber,electronic dispersion compensation,and the use of wavelength tuning control lo
11、ops.addresses reconfigurable free-space optical switches for SANs.It introduces a holographic beam steering optical switch and shutter-based optical switches,and pays attention to optical packet switching for SANs.It is hoped that this feature topic presents a balanced view of developments in indust
12、ry and academia in this rapidly developing field.第15页，本讲稿共29页The vast explosion of data traffic and the growing dependence of the financial world on electronic services have led to a tremendous incentive for SAN services and storage-capable networks.Coupled with a need to store information and Dynam
13、ically reproduce it in real time,SANs are experiencing a new upward thrust.Local SANs based on the intra-office client-server hub-and-spoke model have long been deployed as the de facto standard for backing up servers and high-end computing devices within campuses and premises.Next-Generation Optica
14、l Storage Area Networks:The Light-Trails Approach第16页，本讲稿共29页with the growth of the Internet,back office operations,and a need for secure backup at geographically diverse locations,SANs have moved from their premises confinement to a larger area of proliferation.These new categories of SAN sites,als
15、o known as Internet data centers(IDCs),are becoming increasingly Important from the revenue as well as security perspectives.These sites are connected to one another and to their client nodes through a transport medium.第17页，本讲稿共29页Considering the high volume of data that is transferred between clien
16、ts and servers today,transport is likely to take place across optical communication links.Optical fiber offers large bandwidth for high-volume transfer with good reliability to facilitate synchronousbackup capabilities between SAN sites and clients or between multiple SAN sites in server mirroring o
17、perations.Currently,optical channels are used only for transport of information,while standardized protocols such as Fibre Channel,ESCON,and FICON operate at the data layer,enabling actual transfer of information.第18页，本讲稿共29页With the sharp rise in the need for dynamic services,future SAN systems sho
18、uld be able to cater todynamic provisioning of“connections”betweenserver sites and clients.Bandwidth provisioning in a low-cost setup is the key challenge for future SAN systems.The most natural way to facilitate these services is to enable a protocol Residing hierarchically over the data layers,fac
19、ilitatingthe necessary dynamism in bandwidth arbitrationas well as guaranteeing quality of service(QoS)at the optical layer.第19页，本讲稿共29页This,however,complicates the process and leads to expensive solutions as nodes then would have to perform hierarchical protocol dissemination.The optical layer that
20、 has so far been used primarily just for transport can,however,be pushed further to satisfy some of the cutting-edge needs of next-generationSAN systems.These include multicasting for multisite mirroring,dynamic provisioning for low-cost asynchronous by timely backup,and providing a low-cost system
21、that takes advantage of the reliability and resiliency of the Optical layer.第20页，本讲稿共29页Figure1.The conceptual differences between a lightpath and a light-trail,and the architecture of a light-trail node.The first node is the convener node,the last node is the end node.The light-trial,which essentia
22、lly resides on a wavelength,is optically switched between these two nodes.Multiple light-trails can use the same wavelength as long as the wavelengths do not overlap,thereby leading to spatial reuse of the wavelength.Light-trails present a suitable solution for traffic grooming.Multiple nodes can sh
23、are an opened wavelength in an optimum way to maximize the wavelengths utilization.第21页，本讲稿共29页A light-trail is a generalization of a lightpath(optical circuit)in which data can be inserted or removed at any node along the path.Light-trails are a group of linearly connected nodes Capable of achievin
24、g dynamic provisioning in an opticalpath through an out-of-band control channel(overlaid protocol).This leads to multiple source-destination pairs able to establish time differentiated connections over the path while eliminating the need for high-speed switching.第22页，本讲稿共29页A light-trail is characte
25、rized by a segment of nodes that facilitate unidirectional communication.A node in a light-trail employs the drop-and-continue feature,which allows nodes to Communicate to one another through non-time-overlapping connections without optical switching.The switchless aspect makes a light-trail analogo
26、us to an optical bus.However,a light-trail,due to its out-of-band protocol,enhances the known properties of an optical bus.第23页，本讲稿共29页第24页，本讲稿共29页Consider an n-node light-trail A1,An as shown in Fig.2.assume that each node is connected to a SAN interface like Fibre Channel.assume that k of these n
27、nodes are client nodes(sources),and the remaining n k nodes are servers(primarily sinks)that store the data somewhat in real time(synchronously).Data that arrives at the k SAN client interfaces from theirclient network is buffered in the Fibre Channel interface buffers that are typically 8256 Mb,and
28、 are used to store the data until an acknowledgment of successful transport of this data is received.第25页，本讲稿共29页to suit the dynamic provisioning of the light-trail system,we make a small deviation from the generic Fibre Channel specification,allocating exactly one more buffer(of the same size as us
29、ed by the Fibre Channel interface)at each client node site(Fig.2).This extra buffer is collocated with and the mirror of the original buffer.The critical aspect of this network then is to optimally use the opened single wavelength(light-trail)to ensure communication among n nodes unidirectionally(to
30、 complete duplex we need another light-trail,not shown in Fig.2 topreserve clarity).第26页，本讲稿共29页Disaster recovery implementations for SAN using Fibre Channel over WDM and SAN using light-trails.Note the apparent fewer number of wavelengths required in the light-trail case.第27页，本讲稿共29页第28页，本讲稿共29页第29页，本讲稿共29页