Installation guide

Chapter 9. Diagnosing and Correcting Problems in a Cluster
Clusters problems, by nature, can be difficult to troubleshoot. This is due to the increased complexity
that a cluster of systems introduces as opposed to diagnosing issues on a single system. However,
there are common issues that system administrators are more likely to encounter when deploying or
administering a cluster. Understanding how to tackle those common issues can help make deploying
and administering a cluster much easier.
This chapter provides information about some common cluster issues and how to troubleshoot them.
Additional help can be found in our knowledge base and by contacting an authorized Red Hat
support representative. If your issue is related to the GFS2 file system specifically, you can find
information about troubleshooting common GFS2 issues in the Global File System 2 document.
9.1. Configurat ion Changes Do Not T ake Effect
When you make changes to a cluster configuration, you must propagate those changes to every
node in the cluster.
When you configure a cluster using Co n g a, Co n g a propagates the changes automatically when
you apply the changes.
For information on propagating changes to cluster configuration with the ccs command, refer to
Section 5.15, “Propagating the Configuration File to the Cluster Nodes” .
For information on propagating changes to cluster configuration with command line tools, refer to
Section 8.4, “ Updating a Configuration” .
If you make any of the following configuration changes to your cluster, it is not necessary to restart
the cluster after propagating those changes the changes to take effect.
Deleting a node from the cluster configuration—except where the node count changes from
greater than two nodes to two nodes.
Adding a node to the cluster configuration—except where the node count changes from two nodes
to greater than two nodes.
Changing the logging settings.
Adding, editing, or deleting HA services or VM components.
Adding, editing, or deleting cluster resources.
Adding, editing, or deleting failover domains.
If you make any other configuration changes to your cluster, however, you must restart the cluster to
implement those changes. The following cluster configuration changes require a cluster restart to
take effect:
Adding or removing the two _no d e option from the cluster configuration file.
Renaming the cluster.
Changing any co ro sync or openai s timers.
Adding, changing, or deleting heuristics for quorum disk, changing any quorum disk timers, or
changing the quorum disk device. For these changes to take effect, a global restart of the
q d i skd daemon is required.
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