Restore Concepts; Multiplexing Restores - VERITAS NetBackup White Paper

Restore Concepts

Client users can, at any time, browse their backed up files and select the ones they want to restore. When a user initiates a
restore, the request passes from the client to the master server. Once the server validates the request, the restore operation
becomes fully managed by the server, which identifies the storage device and volume containing the backed up files by
querying the backup catalog. The server then automatically transmits the files back to the client disk.
The process VERITAS NetBackup uses to retrieve images from secondary storage depends on whether the 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. When the media is mounted, the VERITAS NetBackup server reads
the backed up data from the media and sends the requested portions of the image to the client.
When restoring files backed up to magnetic disk, VERITAS NetBackup finds the image path stored in its file database during
the backup operation, and sends the requested portions of the image to the client. The disk manager handles the actual
reading of backed up data from the disk file.
Figure 19 shows the data flow in restore operations.
Figure 19: NetBackup restore data flow.

Multiplexing Restores

VERITAS NetBackup supports the parallel multiplexed (simultaneous) restore of multiplexed backup images. To enable
multiplexed restore, the tape must have been written with multiplexing enabled during the backup. Any subset of the
number of "plexes" of the backup multiplexes may be restored in parallel. For example, if five backup sessions were
multiplexed to the tape during the backup, any number of backup sessions up to the five could be restored in parallel with a
single pass of the tape.
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