Replication is the technique of using multiple copies of a server or a resource for better availability and performance. Each copy is called a replica.
The main goal of replication is to improve availability, since a service is available even if some of its replicas are not. This helps mission critical services, such as many financial systems or reservation systems, where even a short outage can be very disruptive and expensive. It helps when communications is not always available, such as a laptop computer that contains a database replica and is connected to the network only intermittently. It is also useful for making a cluster of unreliable servers into a highly-available system, by replicating data on ...