StorageTek 6 manual LMU Server Functions, Dual LMU Functionality, If the Master LMU Fails

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

66VM/HSC 6.0 System Programmer’s Guide

1st ed., 6/30/04 - 312579601