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66 VM/HSC 6.0 System Programmer’s Guide
1st ed., 6/30/04 - 312579601
LMU Server Functions
LMU server functions control each of the Automated Cartridge Systems within a library.
Many of the LMU server functions are completely transparent to users. This section
contains information about LMU server tasks of which you should be aware.
Dual LMU Functionality
With dual LMU functionality, a switch happens when the LMU designated as the master
fails, or is forcibly switched by issuance of an operator command. The operator is also
notified when the LMU designated as the standby fails.
If the Master LMU Fails
When the master LMU fails:
• the standby LMU detects the failing master and informs the HSC
• the HSC reports the failure by issuing a message
• the HSC reacts as necessary to recover and continue processing mounts and
dismounts.
If the Standby LMU Fails
The standby LMU constantly polls the master. The master LMU acknowledges this
polling.
In the communications between the HSC and the master LMU, the master, as part of its
acknowledgment, informs the HSC of the status of the standby. The standby LMU is either
ready or not ready.
The master LMU thinks that the standby is ready if the standby has polled the master in
the required time interval. If the standby LMU has not polled the master in the required
time interval, the master informs the HSC that the standby is not ready.
The HSC issues an outstanding message. This informs the operator of the status change
(not ready) in the standby LMU.
Operator Control of LMUs
A library operator can control which LMU is operating with the SWitch command. When
the SWitch command is issued, all hosts connected to the ACS are affected.
If after entering a SWitch command, the new master LMU fails and the switchover does
not occur in 20 seconds, the HSC attempts to resume working with the old master. (The
HSC has been waiting for the standby LMU to take over as the master LMU, but the
switch did not take place.)
If the SWitch command fails, the system issues an error message. The operator can force
the completion of the command-generated switchover either by:
• manually re-IPLing the master LMU, or
• powering off the master LMU. 2