Consequences Of An Lmu Switch; Performing An Automatic Lmu Switch; Performing An Operator-Started Lmu Switch - StorageTek 4410 Hardware Operator's Manual

LMU Operation

Consequences of an LMU Switch

When an LMU switch occurs, console messages track the changing status of the master
and standby LMUs.
When a switch occurs in a dual LMU environment, the software questions the LMUs to
determine the current status of each station. The status of each station is kept as online,
offline, standby, pending online, pending offline, or pending force offline. Use the
command to display the ACS status to determine the status of each station, as well as the
status of each LMU.

Performing an Automatic LMU Switch

LMU firmware detects, reports, and reacts to LMU failures as necessary to keep the ACS
working. You have no control over the timing of an automatic LMU switch; therefore,
some work might be in process within the LMU.
When the standby LMU takes over as master, it notifies the software of its status and
sends the LMU ready signal. The software reads the recovery information that is
provided by the new master LMU concerning in-transit cartridges within the various
LSMs in the ACS.
The firmware:
1. Marks completed the queued requests, reflecting the current locations of in-transit
cartridges
2. Sends all incomplete requests to the new master LMU
3. Marks cartridges as errant when requests cannot be completed successfully
Note: You might need to restart enter and eject operations after an LMU switch.

Performing an Operator-started LMU Switch

Before you start an LMU switch while some stations are communicating, decide if the
need to switch LMUs is immediate, or if processing can complete before you make the
switch. If the need to switch LMUs is not critical, wait until the LSMs are relatively idle.
Start an LMU switch by typing the switch command. The command is routed through
the standby LMU to the disconnected master LMU, causing it to IPL. The following
sequence of events occurs:
1. The software sends the switch message.
2. The standby LMU becomes the master LMU; the Master indicator turns on.
3. Online LSMs perform a quick initialization.
4. As each LSM becomes ready, the firmware sends a message.
5. If the old master LMU completes IPL successfully, it becomes the standby LMU.
3-64 Eleventh Edition 9206