HP StorageWorks XP Cluster Extension Software Administrator Guide (T1656-96035, April 2010)

A failover domain can have the following characteristics:
• Unrestricted: Specifies that the subset of members is preferred, but the cluster service assigned to
this domain can run on any available member.
• Restricted: The cluster service is allowed to run only on a subset of failover domain members.
• Unordered: The member on which the cluster service runs is chosen from the available list of failover
domain members with no preference order.
• Ordered: The failover domain member on which the cluster service runs is selected based on
preference order. The member at the top of the list (as specified in /etc/cluster/
cluster.conf) is the most preferred, followed by the second member, and so on.
For an orderly failover, HP recommends using the Ordered and Restricted options for your failover
domains.
Failback policy
HP does not recommend auto failback in configurations with XP Cluster Extension because the resource
failovers due to storage failure can cause resources to go into an unstable state (failover/failback
might toggle the resource between the nodes). In this situation, HP recommends correcting the failure
and then manually failing back to the intended data center or server.
To disable the auto failback, set the nofailback flag for the failover domain.
Enabling this option for an ordered failover domain prevents automated failback after a more-preferred
node rejoins the cluster.
Recovery policy
When a resource inside the service fails, the default action is to restart the service on the local node
before the failover. In an XP Cluster Extension environment, it is always expected to relocate the
service during restart. To enable this functionality, set the service recovery policy to relocate.
Service hierarchical structure and resource dependency
In RHCS, a service is a collection of cluster resources configured into a single entity that is managed
(started, stopped, or relocated) for high availability. A service is represented as a resource tree that
specifies each resource, its attributes, and its relationship among other resources in the resource tree.
The relationships can be parent, child, or sibling. Even though a service is seen as a single entity, the
hierarchy of the resources determines the order in which each resource within the service is started
and stopped.
In the case of a child-parent relationship, the startup or shutdown is simple. All parents are started
before children, and children must all stop cleanly before a parent can be stopped. For a resource
to be considered in good health, all of its children must be in good health.
A service is considered failed if any of its resources fail. In this case, the expected course of action
is to restart the entire service, including the failed resource and the other resources that did not fail.
In an XP Cluster Extension environment, configure the XP Cluster Extension resource as the parent
resource in the service so that XP Cluster Extension can control the service behavior based on the user
configuration and storage device status. This means that the XP Cluster Extension resource must be
configured at the highest level in the dependency hierarchy.
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