HP 3PAR Cluster Extension Software Administrator Guide (5697-2047, June 2012)

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 HP 3PAR 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 a HP 3PAR 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 a HP 3PAR Cluster Extension environment, configure the HP 3PAR Cluster Extension resource as
the parent resource in the service so that HP 3PAR Cluster Extension can control the service behavior
based on the user configuration and storage device status. This means that the HP 3PAR Cluster
Extension resource must be configured at the highest level in the dependency hierarchy.
Disk monitoring
For the situations in which disk access is lost or read/write protection is in effect due to storage
fencing, application monitoring agents, file system agents, or LVM resource agents detect the IO
failure. HP 3PAR Cluster Extension does not monitor the disk access status.
18 HP 3PAR Cluster Extension features