Multiplexing Backups - VERITAS NetBackup White Paper

Figure 15: Backup data flow.
In all cases, the client generates the backup image as a data stream using TCP/IP sockets and sends it to either the VERITAS
NetBackup master or media server. The receiving server directs the data stream to the appropriate attached storage device.
While the backup operation is progressing, the client directs another data stream to the master server which catalogs information
about the files contained in the backup image and is stored in the NetBackup image catalog. The image catalog and other
VERITAS NetBackup databases are backed up in a separate operation, explained under "Crash Recovery" section below.
The process VERITAS NetBackup uses to write images to secondary storage depends on whether the target storage unit is a
disk file or a peripheral managed by Media Manager. In the latter case, Media Manager assists the backup operation by
handling the volume and drive allocation and mounting as explained later under "Media Manager." VERITAS NetBackup
records the volume information in its file database for use during a subsequent restore.
When backing up to magnetic disk, VERITAS NetBackup writes images to the file path specified during configuration of that
storage unit and records the path of the image in its file database. The disk manager handles the actual writing of data in
the disk file.

Multiplexing Backups

NetBackup can run multiple backups simultaneously and stream the data to one or more devices. The backup streams can be
from locally attached disks or from multiple clients over the network.
As jobs finish, NetBackup dynamically adds more to the device. Sites can tune the configuration to the level of multiplexing
desired on each device and for each schedule.
Multiplexing can dramatically increase performance and allow implementation of a few fast devices, instead of many slow
devices. This optimizes the usage of high-speed tape devices and improves overall performance and data availability.
In conjunction with multiplexed backups, NetBackup also restores multiplexed tape images in parallel. Please see the
multiplexed restore section below for more details.
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