虚网络数据管理协议(1)

 It has been a decade since the first version of the Network Data Management Protocol was launched as an effort to solve the problems posed by the backup and recovery of network file servers. Initial work on the standard was spearheaded by Intelliguard Software (subsequently rolled into Legato Software and EMC Corp.), which produced storage management software, and Network Appliance Inc., which manufactures network file servers.
　　The standard was developed to address the fact that network file servers are not able to use the storage device drivers designed for general-purpose computers. They are specialized appliances that connect to a network and are optimized to perform a single set of tasks. Their files are usually mounted by general-purpose computers through protocols such as the Unix/Linux Network File System and Microsoft Windows Common Internet File System.
　　Without NDMP, there were two choices for backing up network file servers. One was to mount their file systems onto the file system of a computer across the network and do the backup there. The downside was that backup and restore required network and server bandwidth. Moreover, the added complexity made it difficult to use optimized aspects of the network file server, such as Network Appliance's Snapshot capability.
　　The other option was to write driver software for each type of network file server and locally attached storage system (tape drives, jukeboxes, CD-ROM writers). That required vendors (manufacturers of network file systems and storage systems and/or backup control software houses) to produce multiple driver variants.
　　The advantage of NDMP is that it establishes a single set of interfaces between the three components involved in a backup or restore operation--the software controlling the backup or restore, the source medium and the destination medium. When all the components are NDMP-compliant, the manufacturer of each can concentrate on maximizing the efficiency of its side of the interface.
　　By 1999, the time for backing up an Oracle database residing on one of Network Appliance's network file servers had been reduced from hours to minutes. Instead of mounting the network file server's files to the computer acting as an Oracle server, the backup was done locally on the network file server and used Network Appliance's Snapshot files, which allow for live backup of a consistent disk image.
　　The paradigm for NDMP is a client/server architecture in which data producers and consumers are thought of as servers or service providers, and the backup control software is thought of as a client. There is one client per NDMP session. There can be multiple servers. In NDMP documentation, clients are also sometimes called data management applications, and servers or service providers are called data service providers (DSP).
　　A DSP such as a network file server produces a data stream when it provides data to a storage system for backup. It consumes data when a storage system provides it with data for a restore. (To Be Continued)

虚网络数据管理协议(1)

　　网络数据管理协议第一版问世以来已有十年了，它是为解决因服务文件服务器的备份和恢复带来的问题而开发的。最初是由Intellguard软件公司（后来它合并到了Legato软件和EMC公司）和Network Appliance公司率先进行此标准的研究，前者提供存储管理软件，而后者制造网络文件服务器。
不用NDMP，备份网络文件服务器有两种选择。一是将网络文件服务器的文件系统通过网络装入一台计算机的文件系统，在这台计算机上进行备份。其缺陷是备份和恢复需要消耗网络和服务器的带宽。而且，增加的复杂度使利用网络文件服务器的优化功能很困难，如Network Appliance公司的"快照"功能。
NDMP的优点就是在备份或恢复操作中涉及的三样东西（控制备份或恢复的软件、源介质和目的介质）之间建立一组单一的接口。当这些东西都符合NDMP时，每样东西的制造商就能集中精力最大程度地提高接口里面的效率。
NDMP模式是一种客户/服务器架构，其中数据生产者和消费者被认为是服务器或服务提供者，而备份控制软件被认为是一个客户。每一次NDMP会话只有一个客户，但可以有多个服务器。在NDMP的文档中，客户有时也叫做数据管理应用，服务器或服务提供商叫做数据服务提供者（DSP）。