Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 4.7 Overview page 18

Chapter 1. Red Hat Cluster Suite Overview
• Configured with CMAN/DLM —
• Configured with GULM servers — GULM performs fencing.
When the cluster manager determines that a node has failed, it communicates to other
cluster-infrastructure components that the node has failed. The fencing program (either
or GULM), when notified of the failure, fences the failed node. Other cluster-infrastructure
components determine what actions to take — that is, they perform any recovery that needs to
done. For example, DLM and GFS (in a cluster configured with CMAN/DLM), when notified of a
node failure, suspend activity until they detect that the fencing program has completed fencing
the failed node. Upon confirmation that the failed node is fenced, DLM and GFS perform
recovery. DLM releases locks of the failed node; GFS recovers the journal of the failed node.
The fencing program determines from the cluster configuration file which fencing method to use.
Two key elements in the cluster configuration file define a fencing method: fencing agent and
fencing device. The fencing program makes a call to a fencing agent specified in the cluster
configuration file. The fencing agent, in turn, fences the node via a fencing device. When
fencing is complete, the fencing program notifies the cluster manager.
Red Hat Cluster Suite provides a variety of fencing methods:
• Power fencing — A fencing method that uses a power controller to power off an inoperable
node
• Fibre Channel switch fencing — A fencing method that disables the Fibre Channel port that
connects storage to an inoperable node
• GNBD fencing — A fencing method that disables an inoperable node's access to a GNBD
server
• Other fencing — Several other fencing methods that disable I/O or power of an inoperable
node, including IBM Bladecenters, PAP, DRAC/MC, HP ILO, IPMI, IBM RSA II, and others
Figure 1.4, "Power Fencing Example"
fencing program in node A causes the power controller to power off node D.
Channel Switch Fencing Example"
example, the fencing program in node A causes the Fibre Channel switch to disable the port for
node D, disconnecting node D from storage.
8
, the fence daemon, performs fencing.
fenced
shows an example of power fencing. In the example, the
shows an example of Fibre Channel switch fencing. In the
fenced
Figure 1.5, "Fibre