信息存储材料与技术.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,光电子存储材料和技术,许立新,光存储,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。,激光全息：实现三维图像存储不能进行实时数据存取。,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。,光盘存储器（简称,“,光盘,”,）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，通过铝膜上极细微的凹坑记录信息。,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：,数据一旦进入光盘，所占的空间是不能释放的。,可读写光盘：,也已投放市场。,光盘,的结构特点和工作原理,光盘,和工作原理,光盘表面：,0/1,光盘外观,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,偶氮,光存储基本原理,光烧孔,：光物理烧孔、光化学烧孔,电子俘获,It is estimated that the human race has created about 1,exabyte,(1018)of information to date.,It is also,predictedthat,the next,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 growth in,geographically,geographically,dispersed online activities.,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 developed,and optimized with data storage in mind,although it is,now realized that they represent the main solution,availabletoday,for networking geographically dispersed,storage and users.,Fabric attached storage,which includes storage area,networks(,SANs,)and network attached storage(NAS),represents one of the fastest 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,reconfigurability,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.,considers next-generation optical storage area networks,based on the light-trails approach 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 extensions.,considers dispersion compensation for,SANs,where data,centers still use legacy,multimode fiber with a limited bandwidth-distance,product.The article discusses the use of enhanced,Bandwidth multimode fiber,electronic dispersion,compensation,and the use of wavelength tuning control,loops.,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 industry and academia in this rapidly,developing field.,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,Dynamically 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 Optical Storage Area Networks:The Light-Trails Approach,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,also 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.,Considering the high volume of data that is transferred,between clients 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 synchronous,backup capabilities between SAN sites and clients or,between multiple SAN sites in server mirroring,operations.,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.,With the sharp rise in the need for dynamic services,future SAN systems should be able to cater to,dynamic provisioning of“connections”between,server 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,facilitating,the necessary dynamism in bandwidth arbitration,as well as guaranteeing quality of service(,QoS,)at the,optical layer.,This,however,complicates the process and leads to,expensive solutions as nodes then would have to,perform hierarchical protocol dissemination.,The optical layer that has so far been used primarily just,for transport can,however,be pushed further to satisfy,some of the cutting-edge needs of next-generation,SAN systems.,These include multicasting for,multisite,mirroring,dynamic provisioning for low-cost asynchronous by,timely backup,and providing a low-cost system that,takes advantage of the reliability and resiliency of the,Optical layer.,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 essentially 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 share an opened wavelength in an optimum way to,maximize the wavelengths utilization.,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 achieving dynamic provisioning in an optical,path 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.,A light-trail is characterized 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 analogous to an,optical bus.However,a light-trail,due to its out-of-band,protocol,enhances the known properties of an optical,bus.,Consider an,n,-node light-trail,A,1,A,n,as shown in Fig.2.assume that each node is connected to a SAN interface like,Fibre,Channel.,assume that,k,of these,n,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 their,client network is buffered in the,Fibre,Channel interface buffers that are typically 8256 Mb,and are used to store the data until an acknowledgment of successful transport of this data is received.,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 used 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 complete duplex we need another light-trail,not shown in Fig.2,topreserve,clarity).,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.,