On more advanced clusters, this takeover can happen in milliseconds. The performance advantage of clusters stems from an ability to load balance across multiple systems. The servers can be set up to operate in parallel, giving a near-linear increase in performance capacity. Finally, clusters can enable simple multiserver management. To a manager, a cluster can work as a single system.
Clustering takes many forms, and can scale from two computers.
The fundamental principle is the same for all cluster sizes, but each computer in the cluster should be able to take up the duties of other computers in the cluster should they fail. The simplest clusters are fail-overs. Redundant systems are available should the main server fail. Clusters that are more complex use load-balancing systems to divide work among available nodes. If one of the servers fails, the load is redistributed across the remaining systems.