AppAssure

Replication Software

Replication is the process of sharing information in order to ensure consistency between redundant resources, such as software or hardware components, so as to improve accessibility, fault-tolerance, or reliability. It could be computation replication if the same computing task is executed many times or data replication if the same data is stored on multiple storage devices. A computational task is typically replicated in space, i.e. executed on separate devices, or it could be replicated in time, if it is executed repeatedly on a single device.

It is common to talk about active and passive replication in systems that replicate data or services. Active replication is performed by processing the same request at every replica. In passive replication, each single request is processed on a single replica and then its state is transferred to the other replicas. If at any time one master replica is designated to process all the requests, then we are talking about the primary-backup scheme (master-slave scheme) predominant in high-availability clusters. On the other side, if any replica processes a request and then distributes a new state, then this is a multi-primary scheme (called multi-master in the database field). In the multi-primary scheme, some form of distributed concurrency control must be used, such as distributed lock manager.

Replication is an enhancement of Backup since replicas are easily accessible and are frequently updated and quickly lose any historical state.