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| How VCS Replicated Data Clusters work | ||
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To understand how a RDC configuration works, let us look at an application configured in a VCS replicated data cluster.
The configuration has two system zones:
Primary zone (zone 0) comprising nodes located at the primary site and attached to the primary storage
Secondary zone (zone 1) comprising nodes located at the secondary site and attached to the secondary storage
The application is installed and configured on all nodes in the cluster. The application data is located on shared disks within each RDC zone and is replicated across RDC zones to ensure data concurrency. The application service group is online on a system in the current primary zone and is configured to fail over in the cluster.
If the system or application fails, VCS attempts to fail over the application service group to another system within the same RDC system zone. However, if VCS cannot find a failover target node within the primary zone, VCS switches the service group to a node in the current secondary system zone (zone 1). VCS also redirects clients once the application is online on the new location.
While this example required using shared storage, you can also set up an RDC cluster that uses non-shared storage. This involves installing and configuring the application on a single system in each of the RDC zones. The application data is located on the local disks attached to the system within each RDC zone. The data is replicated between the systems across the RDC zones to ensure concurrency.
The application service group is online on the single node in the primary RDC zone (Zone 0). In the event of a failure, VCS switches the service group to the node in the secondary RDC zone (Zone 1). Data replication ensures that the application is able to successfully handle client requests from the new node.
The following figure shows failover in a replicated data cluster using non-shared storage.
