By inter-connecting multiple servers many times with access to shared resources, the resulting cluster is able to deliver greater availability. This increase in availability is due to the ability of the other systems in a cluster to assume the workload of a failing system resource. Likewise, maintaining access to data is a key element for high availability. If your server is running but it can't reach critical data, your business may cease to function. Properly designed cluster solutions can also reduce or eliminate planned outages due to hardware or software upgrades by allowing selected systems to be taken off-line for nondisruptive upgrades.
Clusters are also a key element for most disaster recovery solutions.
When one site is no longer available due to a serious disaster, a backup location can quickly become available to resume work with minimal interruption. IBM has demonstrated leadership cluster solutions for both high availability as well as disaster recovery across its server family and continues to enhance these solutions. For end users, availability is much more than hardware fail-over capabilities. Without application availability, one cannot achieve mission-critical HA solutions. A cluster-aware application is able to initiate an orderly transition to a backup node in the event of failure as well as use cluster tools to take corrective action to prevent a failure.