Symantec NetBackup - About the Device Allocation Host; About Reserving or Releasing Shared Devices

For shared tape drives, only the scan host polls drives until
a mount request is received from NetBackup. During a
mount request, NetBackup uses the host that requests the
mount to poll the shared drive.
This design enables NetBackup to support Dynamic Loop
Switching or SAN zones. Each tape drive needs to be
detected only from a single host. Each tape drive can
potentially have its own scan host that switches dynamically
to process errors and continue availability. A central device
arbitrating component manages scan host assignments for
shared drives. The arbitrating component also provides a
network drive reservation system so that multiple
NetBackup media servers can share a drive.
Polling a shared tape drive allows dynamic loop switching
and reduces the number of device accesses and reduces CPU
time. However, it cannot detect connectivity breaks (for
example, discontinuity in the Fibre Channel fabric) until
I/O occurs.
Shared tape drive polling
About the device allocation host
The device allocation host is another name for the EMM server, when the EMM
server performs device allocation tasks for Shared Storage Option.
About reserving or releasing shared devices
The Shared Storage Option does not load firmware in SAN devices or communicate
with hub or switch APIs. The Shared Storage Option can communicate with hub
or switch APIs if you use the NetBackup shared_drive_notify script.
NetBackup runs the shared_drive_notify script when a shared drive is reserved
or released.
The script requires the following parameters:
■ The name of the shared drive.
■ The name of the current scan host.
■ The operation, which is one of the following:
The host on which the script is executed needs SCSI access to the
drive until it is released.
RESERVED
141Introducing the Shared Storage Option
About reserving or releasing shared devices