As it relates to server technology, a cluster refers to two or more computers working cohesively to deliver a higher level of scalability and reliability than can be achieved with a single machine.  Cluster servers are primarily used to help prevent three types of failure:


1.) Application and service failures that impact software applications and critical services.


2.) System and hardware failures that impact server components, such as hard drives, memory, CPUs, network adapters and power supplies.


3.) Site failures caused by power or connectivity outages or natural disasters.


When optimized to handle such failures, cluster servers are able to meet higher requirements for availability, which simply describes the user’s ability to access a particular service.


How Cluster Servers Work


With cluster servers, each machine owns and manages its local devices.  It also maintains a copy of the operating system, as well as the applications or services the cluster is managing.  Devices relative to the cluster, including disks in common disk arrays along with the connection media used to access them, are owned and managed by one server at a time.


In the average cluster server environment, applications are stored on disks in one of the common disk arrays.  This data can only be accessed by the server with ownership of the corresponding application or service.


The design of cluster servers enables all the servers to work together to protect against data loss, ensure the availability of applications and services even if one server should fail, and maintain the consistency of the cluster. If you are looking to prevent server failure from impacting your online presence, cluster servers are certainly an excellent option.