Local clustering provides local failover for each site or building. But, these configurations do not provide protection against large-scale disasters such as major floods, hurricanes, and earthquakes that cause outages for an entire city or region. The entire cluster could be affected by an outage.
Let us take the example of an Oracle database configured in a VCS global cluster. Oracle is installed and configured in both clusters. Oracle data is located on shared disks within each cluster and is replicated across clusters to ensure data concurrency. The Oracle service group is online on a system in cluster A and is configured to fail over globally, on clusters A and B.
Figure: Sample global cluster setup shows a sample global cluster setup.
VCS continuously monitors and communicates events between clusters. Inter-cluster communication ensures that the global cluster is aware of the state of the service groups that are configured in the global cluster at all times.
In the event of a system or application failure, VCS fails over the Oracle service group to another system in the same cluster. If the entire cluster fails, VCS fails over the service group to the remote cluster, which is part of the global cluster. VCS also redirects clients once the application is online on the new location.