StorageTek Host Software Component 6.0, System Programmer'S Manual

Page: 45 / 718

Chapter 1. System Description 15
1st ed., 6/30/04 - 312579601
In a library configuration containing more than one LSM, if a cartridge exchange
operation occurs to obtain the cartridge for mounting, the cartridge may be returned by
one of these possible ways:
• If the MNTD Float command is set to ON (the HSC initial value), the cartridge is
returned to any new cell location in the LSM containing the tape transport from
which it was dismounted. For more information about the MNTD Float command,
refer to Chapter 2, ‘‘Commands, Control Statements, and Utilities’’ in the
HSC
Operator’s Guide.
• If the MNTD Float command is set to OFF, the cartridge is passed through to the
origin LSM and placed into its originating cell location. For more information about
the MNTD Float command, refer to Chapter 2, ‘‘Commands, Control Statements,
and Utilities’’ in the
HSC Operator’s Guide .
• If the LSM is full, the cartridge is passed thru to another LSM and placed in any cell
location.
• A temporary enter on a mount operation means an eject upon dismount (the cartridge
does not remain in the LSM).
The library control data set is automatically updated to reflect the new location of the
cartridge.
Dual LMU Environment
In a dual LMU environment, the HSC maintains contact with both LMUs. Both LMUs are
varied online. One LMU functions as the master LMU and the other functions as the
standby LMU. Requests and responses are channeled through station paths on the master
LMU. Paths on the standby LMU are online, but not used.
The master LMU continually informs the HSC of the status of the standby LMU. The
HSC informs the operator when status changes.
The standby LMU constantly polls the master LMU. If the master LMU fails, the standby
LMU informs the HSC that status has changed. The standby becomes the master. The
HSC also informs the operator that the previous master LMU is not communicating.
At switchover, the HSC:
• notifies the operator that switchover is occurring
• verifies the configuration for the LMU
• sends the new master LMU all the work that was in progress
• terminates ENTER operations.
After switchover, the HSC sends the new master all ACS requests.
Switchover should not affect movement in process. All moves should complete. If not, the
cartridges become errant and are found when the LSMs perform ‘‘quick initialization’’
processing. ENTER operations must be restarted after switchover.