Implementing a Failover Resource

A failover resource group contains network addresses, such as the built-in resource types LogicalHostname and SharedAddress, and failover resources, such as the data service application resources for a failover data service. The network address resources, along with their dependent data service resources, move between cluster nodes or zones when data services fail over or are switched over. The RGM provides a number of properties that support implementation of a failover resource.

A failover resource group can fail over to a zone on another node or on the same node. However, if the node fails, the failing over of this resource group to a zone on the same node does not provide high availability. Nonetheless, you might find this failing over of a resource group to a zone on the same node useful in testing or prototyping.

Set the Boolean Failover resource type property to TRUE to restrict the resource from being configured in a resource group that can be online on more than one node or zone at a time. The default for this property is FALSE, so you must declare it as TRUE in the RTR file for a failover resource.

The Scalable resource property determines if the resource uses the cluster shared address facility. For a failover resource, set Scalable to FALSE because a failover resource does not use shared addresses.

The RG_mode resource group property enables the cluster administrator to identify a resource group as failover or scalable. If RG_mode is FAILOVER, the RGM sets the Maximum_primaries property of the group to 1. The RGM also restricts the resource group to being mastered by a single node or zone. The RGM does not allow a resource whose Failover property is TRUE to be created in a resource group whose RG_mode is SCALABLE.

The Implicit_network_dependencies resource group property specifies that the RGM should enforce implicit strong dependencies of nonnetwork address resources on all network address resources (LogicalHostname and SharedAddress) within the group. As a result, the Start methods of the nonnetwork address (data service) resources in the group are not called until the network addresses in the group are configured to go up. The Implicit_network_dependencies property defaults to TRUE.