Shared Storage Option (Drive Sharing) - VERITAS NetBackup White Paper

The Device Manager always uses the volume database to get information about the volume. If the request involves a robot,
this information includes the specific robot that has the volume and the slot location of the volume within the robot. The
device then issues a mount command to the robotic daemon controlling that robot, which automatically mounts the
specified volume and returns control to VERITAS NetBackup. No operator intervention is required, provided the required
volume is physically in the robot.
If the volume is not in the robot, the Device Manager alerts the operator by sending a mount request to the console. The
operator then finds the volume and inserts it in the robot so the operation can proceed.
Barcode verification is also supported for robots with barcode readers. This provides an extra measure of confidence that the
correct volume is being mounted.
With a standalone drive, VERITAS NetBackup attempts to use the media that is in the drive. If the drive does not contain
media, the Device Manager alerts the operator by sending a mount request to the console. The operator then finds the
volume, mounts it manually, and assigns it to the request.
The Media Manager allocates a previously unassigned volume to VERITAS NetBackup whenever a new volume is required for
either a standalone or robotic drive. Volumes allocated to VERITAS NetBackup come from the volume pool designated for
the specific backup files, which by default is the NetBackup volume pool. The term volume pool refers to a distinct set of
volumes that are assigned for a specific use.
Volume Pools make it possible to keep only one type of image on a volume. For example, you could create separate pools
for archives and backups. A case where separate volume pools are mandatory is when another application, such as VERITAS
Storage Migrator, is also using Media Manager.
Once a volume is allocated to VERITAS NetBackup, no other application can use it until all images written on the volume
have expired. The VERITAS NetBackup administrator specifies the retention period for the files and can choose to either keep
all images with the same retention period on the same volume or to keep a mix of different retention periods on a volume.
In addition to assigning volumes, the media manager tracks the location of both online and offline volumes and keeps this
information in the volume database.

Shared Storage Option (Drive Sharing)

The NetBackup Shared Storage Option allows individual tape drives (standalone or in a robotic library) to be dynamically
shared between multiple NetBackup master or media servers. Drives can be dynamically allocated across NetBackup servers
as backup/restore operations dictate. This software option requires appropriate hardware connectivity, such as a SCSI
multiplexer or fibre switch/hub storage area network (SAN). If the robotic control is SCSI-based, one host controls the
robotics (see the "Sharing Tape Libraries" section below). Other applications such as VERITAS Storage Migrator and user tape
requests can also share tape drives.
Figure 26 below diagrams an example of a shared drive configuration. Multiple NetBackup servers (master servers or media
servers) are grouped around one or more multi-drive libraries connected by a fibre or SCSI switch. During setup, drives that
are to be shared between NetBackup servers are defined as shared drives by the system administrator. Drives not designated
as shared drives are dedicated to a single server. All of the shared drives are available to any of the NetBackup servers in the
SAN. When a backup session is initiated on a specific NetBackup server, that server requests the appropriate number of
drives from the shared drives available. Assuming the number of requested drives are available, the drives are allocated to
that server, the electrical connection is configured in the switch, and the backup proceeds. When the backup session
completes, the drives are de-allocated, freeing them for use by other NetBackup servers. The same process repeats as other
NetBackup servers initiate backup or restore operations. Once all of the shared drives are allocated, the backup/restore
session is queued until the requested number of drives are available.
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