Critical and Non-Critical Resources

The Critical attribute for a resource defines whether a service group fails over when a resource faults. If a resource is configured as non-critical (by setting the Critical attribute to 0) and no resources depending on the failed resource are critical, the service group will not fail over. VCS takes the failed resource offline and updates the group status to ONLINE|PARTIAL. The attribute also determines whether a service group tries to come online on another node if, during the group's online process, a resource fails to come online.

VCS Behavior Diagrams

This section describes the default functionality of VCS when resources fault. The following illustration displays the symbols used in this section.

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Scenario: Resource with critical parent faults

The service group in the following example has five resources, of which resource R1 is configured as a critical resource.

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When resource R2 faults, the fault is propagated up the dependency tree to resource R1. When the critical resource R1 goes offline, VCS must fault the service group and fail it over elsewhere in the cluster. VCS takes other resources in the service group offline in the order of their dependencies. After taking resources R3, R4, and R5 offline, VCS fails over the service group to another node.

Scenario: Resource with non-critical parent faults

The service group in the following example does not have any critical resources.

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When resource R2 faults, the engine propagates the failure up the dependency tree. Neither resource R1 nor resource R2 are critical, so the fault does not result in offlining the tree or in service group failover.

Scenario: Resource with critical parent fails to come online

In the following example, when a command is issued to bring the service group online, resource R2 fails to come online.

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VCS calls the Clean function for resource R2 and propagates the fault up the dependency tree. Resource R1 is set to critical, so the service group is taken offline and failed over to another node in the cluster.