VCS performance consideration when a system fails

When a system crashes or is powered off, it stops sending heartbeats to other systems in the cluster. By default, other systems in the cluster wait 21 seconds before declaring it dead. The time of 21 seconds derives from 16 seconds default timeout value for LLT peer inactive timeout, plus 5 seconds default value for GAB stable timeout.

The default peer inactive timeout is 16 seconds, and can be modified in the /etc/llttab file.

For example, to specify 12 seconds:

set-timer peerinact:1200


After modifying the peer inactive timeout, you must unconfigure, then restart LLT before the change is implemented. To unconfigure LLT, type lltconfig -U. To restart LLT, type lltconfig -c.

GAB stable timeout can be changed by specifying:

gabconfig -t timeout_value_milliseconds

Though this can be done, we do not recommend changing the values of the LLT peer inactive timeout and GAB stable timeout.

If a system boots, it becomes unavailable until the reboot is complete. The reboot process kills all processes, including HAD. When the VCS process is killed, other systems in the cluster mark all service groups that can go online on the rebooted system as autodisabled. The AutoDisabled flag is cleared when the system goes offline. As long as the system goes offline within the interval specified in the ShutdownTimeout value, VCS treats this as a system reboot. You can modify the default value of the ShutdownTimeout attribute.