Automatic Failover

A failover occurs when a service group faults and is migrated to another system or when a system crashes. For service groups with dependencies, the following actions occur during failover

1. The service group is taken offline along with any of its parent service groups that have an online firm or hard dependency (online local firm, online global firm, online remote firm, or online local hard).
2. A failover target is chosen from the SystemList of the service group based on the failover policy and the restrictions brought by the service group dependencies.

   If the faulted service group is also the parent service group in a service group dependency relationship, the service group dependency has an impact on the choice of a target system. For example, if the faulted service group has an online local (firm or soft) dependency with a child service group that is online only on that system, no failover targets are available.

3. If there are no other systems the service group can fail over to, the child service group and the parents that were taken offline remain offline. Note that for soft dependencies, when child group faults and cannot fail over, the parent group remains online.
4. If there is a failover target, then VCS takes any child service group with an online local hard dependency offline.
5. VCS then checks if there are any conflicting parent service groups that are already online on the target system. These service groups can be parent service groups that are linked with an offline local dependency or online remote soft dependency. In either case, the parent service group is taken offline to enable the child service group to start on that system.
6. If there is any child service group with an online local hard dependency, first the child service group and then the service group that initiated the failover are brought online.
7. After the service group is brought online successfully on the target system, VCS takes any parent service groups offline that have an online local soft dependency to the failed-over child.
8. Finally, VCS selects a failover target for any parent service groups that may have been taken offline during steps 1, 5, or 7 and brings the parent service group online on an available system.
9. If there are no target systems available to fail over the parent service group that has been taken offline, the parent service group remains offline.