虚网络数据管理协议（２）
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NDMP(2)
Data Replication
This agnostic view of whether a data service is a producer or consumer lends itself to data replication. One storage system can provide a data stream that is consumed by an identical storage system, and the data is copied from one system to another.
In the original versions of NDMP, only one data stream was allowed in the transaction between producers and consumers. In Version 5, that requirement has been loosened with the invention of the Translate Service, which sits between producers and consumers and can multiplex data streams. Although it may open up the possibility for all kinds of intermediate translation, its immediate goal was greater efficiency, allowing the faster side of what had been a single producer/consumer pair to chew data from several sources at once.
In an NDMP session, there is always one TCP/IP connection between each service and the software that centrally manages the network’s backup and recovery operations, which is the data management application. NDMP is geared toward facilitating centralized control of backup and recovery operations. The client initiates contact with services via a well-known TCP/IP port and then follows up with a standard command-and-response dialogue, which is effectively a state machine, with the state maintained on the client. The data services are moved through states with names such as “Idle,” “Listen,” “Active” and “Halted.”
Although the basic paradigm for all communication, both control and data, is via TCP/IP, the door is left open for services to realize local efficiencies, such as when a backup device is attached locally or if a system happens to be on a high-speed storage-area network. Up through Version 4, there were several standard network configurations for NDMP backup and restore sessions. In one, the client sits on a server of its own and commands a network file server to back up to a locally attached storage device. In another, the client again sits on a server of its own and commands a file server to back up, but this time to a storage device located elsewhere on the network. The standard configurations for restore are identical, except the data flow goes in the other direction.
Version 5 is concerned with Internet issues, such as security authorization and networks that exist across the Web (which is one of the reasons the NDMP working group has migrated from the Storage Networking Industry Association to the Internet Engineering Task Force). (The End)
虚网络数据管理协议(2)
数据复制
数据服务是生产者还是消费者的不可知性有助于数据复制。一个存储系统可以提供数据流，供同一存储系统消费，这样数据就从一个系统拷贝到另一系统。
在最初的NDMP版本中，生产者和消费者之间的交易中只允许一个数据流。在第5版中，随着“翻译服务”的发明，这个要求放宽了，此服务在生产者和消费者之间，能实现数据流的多路传输。虽然它有可能开放所有种类的中间翻译，但它直接的目标是提高效率，以发扬单一的生产者/消费者对速度较快的优势，同时处理多个来源的数据。
在NDMP会话中，每个服务和集中管理网络备份和恢复操作的软件之间总是有一个TCP/IP连接，这就是数据管理应用。NDMP是用来方便集中控制备份和恢复操作的。客户通过著名的TCP/IP口启动与服务的接触，随后就是标准的命令和响应对话，实际上这就是状态机，在客户端维持此状态。数据服务在各种状态（如空闲、监听、便用和暂停等）之间进行移动的。
虽然所有的（包括控制和数据）通信的基本模式都是通过TCP/IP，但服务的大门是开放着的，以便在诸如备份设备本地连接时或者系统刚好是一个高速存储区域网时，实现本地的高效率。一直到第4版，NDMP备份和恢复会话有几种标准的网络配置。其中一个就是，客户位于自己的服务器上，并命令网络文件服务器备份到本地连接的存储设备。另一种是，客户还是在自己的服务器上，命令文件服务器进行备份，但这时是在位于网络某处的存储设备上备份。恢复的标准配置除了数据流是相反方向外，其他都是一致的。
第5版与互联网的问题有关，如安全认证和存在于Web上的网络等（这就是NDMP工作小组从存储网络工业协会转到互联网工程任务组的理由之一）。(全文结束)
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