Using the Backup Exec for Windows NDMP Option, it is possible to perform backup operations to a tape library as a 3-Way NDMP Backup operation. A 3-Way NDMP Backup operation is where the tape library is not directly connected to the same NDMP Filer/NAS as that containing the data being protected  (as per Figure 1.)

Fig 1: Standard NDMP 3-Way configuration
 

With the latest versions of the NDMP Option, the Backup Exec Media Server can also operate as an NDMP Tape Server, which results in the ability to mix NDMP and non-NDMP data sets into a single job, with the 3-Way NDMP operation using the tape library attached to the Media Server (as per Figure 2.)

Fig 2: Media Server running as NDMP Tape Server
 

Both of the above configurations will experience a small performance drop compared with direct backups, but both configurations are supported by the current versions of Backup Exec for Windows.

A further 3-Way NDMP configuration is possible where the tape library is attached to the NDMP Filer/NAS, but the data being protected by the backup is located on a Windows Server, either on a remote server running the Remote Agent for Windows Servers (RAWS) or on the Media Server itself (as per Figure 3.)

Fig 3: Unsupported 'pseudo 3-Way' configuration
 

This configuration will exhibit an extreme performance drop because the Backup Exec Remote Agent for Windows (RAWS) is not an NDMP Data server.

This scenario is NOT SUPPORTED by current versions of Backup Exec for Windows.

If the NDMP environment is configured in this way, then a redesign of the backup strategy and NDMP topology is required in order to both increase performance and to implement a supported configuration for the NDMP Option