Hardware Management Console Installation and Operations Guide


Using Two HMCs Connected to One Managed System

This chapter describes how to perform operations on two HMCs connected to one managed system.

Each system that supports a Hardware Management Console has two serial port connections, so that you may optionally attach a second HMC to the same system. The benefits of using two HMCs are as follows:


Working with Two HMCs

In configurations with two HMCs, both HMCs are fully active and accessible at all times, enabling you to perform management tasks from either HMC at any time. There is no primary or backup designation.

To avoid basic conflicts, mechanisms in the communication interface between HMCs and the managed systems allow an HMC to temporarily take exclusive control of the interface, effectively locking out the other HMC. Usually this locking is done only for the duration of time it takes to complete an operation, after which the interface is available for further commands. HMCs are also automatically notified of any changes that occur in the managed systems, so the results of commands issued by one HMC are visible in the other. For example, if you select to activate a partition from one HMC, you will observe the partition going to the Starting and Running states on both HMCs.

The locking between HMCs does not prevent users from running commands that might seem to be in conflict with each other. For example, if the user on one HMC selects to activate a partition, and a short time later, a user on the other HMC selects to power off the system, the system will power off. Effectively, any sequence of commands that you can do from a single HMC is also permitted when your environment contains redundant HMCs. For this reason, it is important to carefully consider how you want to use this redundant capability to avoid such conflicts. You might choose to use them in a primary and backup role, even though the HMCs are not restricted in that way.

The interface locking between two HMCs is automatic, is usually of short duration, and most console operations wait for the lock to release without requiring user intervention. However, if one HMC experiences a problem while in the middle of an operation, it may be necessary to manually release the lock. For more information on this task, see Releasing an HMC Lock on the Managed System.


Other Considerations for Redundant HMCs

Because authorized users can be defined independently for each HMC, determine whether the users of one HMC should be authorized on the other. If so, the user authorization must be set up separately on each HMC.

Because both the HMCs provide Service Focal Point and Service Agent functions, connect a modem and phone line to only one of the HMCs, and enable its Service Agent. To prevent redundant service calls enable Service Agent on on only one HMC.

Perform HMC software maintenance separately on each HMC, at separate times, so that there is no interruption in accessing HMC function. This situation allows one HMC to run at the new fix level, while the other HMC can continue to run at the previous fix level. However, the best practice is to move both HMCs to the same fix level as soon as possible.


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