In a Parallel Sysplex® cluster, it is possible to construct a parallel processing environment with no single points of failure. Because all of the systems in the Parallel Sysplex can have concurrent access to all critical applications and data, the loss of a system due to either hardware or software failure does not necessitate loss of application availability.

Peer instances of a failing subsystem executing on remaining healthy system nodes can take over recovery responsibility for resources held by the failing instance. Alternatively, the failing subsystem can be automatically restarted on still-healthy systems using automatic restart capabilities to perform recovery for work in progress at the time of the failure. While the failing subsystem instance is unavailable, new work requests can be redirected to other data-sharing instances of the subsystem on other cluster nodes to provide continuous application availability across the failure and subsequent recovery. This alternatives provide the ability to mask planned as well as unplanned outages to the end user.

Because of the redundancy in the configuration, there is a significant reduction in the number of single points of failure. Without a Parallel Sysplex, the loss of a server could severely impact the performance of an application, as well as introduce system management difficulties in redistributing the workload or reallocating resources until the failure is repaired. In a Parallel Sysplex environment, it is possible that the loss of a server may be transparent to the application, and the server workload can be redistributed automatically within the Parallel Sysplex with little performance degradation. In a Parallel Sysplex environment, events that otherwise would seriously impact application availability, such as failures in central processor complex (CPC) hardware elements or critical operating system components, have reduced impact.

Even though they work together and present a single image, the nodes in a Parallel Sysplex cluster remain individual systems, making installation, operation, and maintenance non-disruptive. The system programmer can introduce changes, such as software upgrades, one system at a time, while the remaining systems continue to process work. This design allows the mainframe IT staff to roll changes through its systems on a schedule that is convenient to the business.