Explanation:
NDMP defines three kinds of services: a data service that interfaces with the primary storage to be backed up or restored, a tape service that interfaces with the secondary storage (primarily a tape device), and a translator service performing translations including multiplexing multiple data streams into one data stream and vice versa. NDMP services interact with each other. The result of this interaction is the establishment of an NDMP control session if the session is being used to achieve control for the backup or restore operation. It would result in an NDMP data session if the session is being used to transfer actual file system or volume data (including metadata). Control sessions are always TCP/IP-based, but data streams can be TCP/lP-or SAN-based. NDMP is more or less NAS-centric and defines a way to back up and restore data from a device, such as a NAS appliance, on which it is difficult to install a backup software agent, in the absence of NDMP, this data must be backed up as a shared drive on the LAN, which is accessed via network file protocols, such as Common Internet File System (CIFS) or Network File System (NFS), degrading backup performance. NDMP works on a block level for transferring payload data (file content) but metadata and traditional file system information needs to be handled by legacy backup systems that initiate NDMP data movement. NDMP does not know about nor takes care of consistency issues regarding related volumes (e.g., a volume to store database files, a volume to store application server data and a volume to store web server data). NDMP can be used to do backups in such an environment (e.g., SAP) but the logic required either must be put into a dedicated piece of software or must be scripted into the legacy backup software.