Replication

Data replication occurs when the same information is placed in multiple storage devices. Computation replication occurs when a task is executed several times. Computational tasks are generally replicated in disk space, executed on a separate device, or executed repeatedly over a single device. Active and passive replication is a process that occurs in systems that replicate data. Active replication occurs when the same requests are processed. In passive replication, every request is processed individually and then transferred to other replicas. If a master replica is ever designated to process each request, the process is known as a primary-backup scheme. Backup schemes are different from replication in how it saves data copies that may have not been changed for a long period of time. This allows the replicas to be regularly updated and lose their historical state. Replication is typically hidden from a user. In the case of a failure, replicas are very difficult to find on an operating system.