Operating An Lmu-Dual Lmu Configuration; Dual Lmu Operation Overview; Powering On/Ipling An Lmu-Dual Lmu Configuration - StorageTek 4410 Hardware Operator's Manual

LMU Operation
Operating an LMU—Dual LMU Configuration
The following sections describe how to operate dual LMUs.

Dual LMU Operation Overview

Dual LMU configurations provide a backup LMU that can take over if the active (master)
LMU fails. Both LMUs are capable of being the master, but only one can be the master at
a given moment. The LMUs regularly check the status of each other over the local area
network (LAN).
The software directs all input/output (I/O) to the master LMU. All stations may be
placed online to both LMUs when you start the software. The stations to the current
master LMU come fully online, and the stations to the current standby LMU come up as
standby.
Note: It is recommended that you place two stations online to each LMU from each
The requirements for a fully functional dual LMU configuration are:
• LMU firmware level 2.3 or higher
• Correct operating software level (refer to the appropriate software manual)
• Both LMUs powered on (one serves as the master, and the other as the standby)
• At least one station online to each LMU from each host (online stations to a standby
LMU are called standby stations)
If the above conditions are met, an automatic LMU switch can occur if a failure is
detected in the master LMU.
You can use the switch command to manually switch the master LMU functionality to
the standby LMU. You may give the switch command even if no LMU internal errors are
present.
Note: When you enter the switch command, remember that all hosts connected to the
Powering On/IPLing an LMU—Dual LMU Configuration
When an LMU is powered on in a dual LMU environment, it places itself in a standby
status and then checks for an active master LMU. If an active master LMU exists, the
LMU remains available as the standby LMU. If an active master LMU does not exist, the
LMU becomes the master LMU.
If both LMUs are powered-on at about the same time, the first to complete IPL assumes
the role of master. If you prefer to call out one LMU as the master, power it on first and
wait for it to complete IPL before you power-on the second LMU. The following
procedure describes this type of dual LMU power on.
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host. An automatic LMU switch occurs only in response to a failure in the master
LMU. Path failures do not start an LMU switch.
dual LMU ACS are affected by a switch of the master LMU functionality. You
must restart enter operations after an LMU switch.
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