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, which is in the proposal stage this year, 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 towards 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).