Symmetric or active / active configuration

In a symmetric configuration, each server is configured to run a specific application or service and provide redundancy for its peer. In this example, each server runs one application service group. When a failure occurs, the surviving server hosts both application groups.

Figure: Symmetric failover shows failover within a symmetric cluster configuration.

Figure: Symmetric failover

Symmetric failover

Symmetric configurations appear more efficient in terms of hardware utilization. In the asymmetric example, the redundant server requires only as much processor power as its peer. On failover, performance remains the same. In the symmetric example, the redundant server requires adequate processor power to run the existing application and the new application it takes over.

Further issues can arise in symmetric configurations when multiple applications that run on the same system do not co-exist properly. Some applications work well with multiple copies started on the same system, but others fail. Issues also can arise when two applications with different I/O and memory requirements run on the same system.