## Replication 

A replica set in MongoDB is a group of mongod processes that maintain the same data set. Replica sets provide redundancy and high availability, and are the basis for all production deployments. This section introduces replication in MongoDB as well as the components and architecture of replica sets. The section also provides tutorials for common tasks related to replica sets. 

Replication Introduction (page 559) An introduction to replica sets, their behavior, operation, and use. 

Replication Concepts (page 563) The core documentation of replica set operations, configurations, architectures and behaviors. 

Replica Set Members (page 564) Introduces the components of replica sets. 

Replica Set Deployment Architectures (page 572) Introduces architectural considerations related to replica sets deployment planning. 

Replica Set High Availability (page 580) Presents the details of the automatic failover and recovery process with replica sets. 

Replica Set Read and Write Semantics (page 585) Presents the semantics for targeting read and write opera- tions to the replica set, with an awareness of location and set configuration. 

Replica Set Tutorials (page 602) Tutorials for common tasks related to the use and maintenance of replica sets. 

Replication Reference (page 651) Reference for functions and operations related to replica sets. 

## 9.1 Replication Introduction 

Replication is the process of synchronizing data across multiple servers. 

## 9.1.1 Purpose of Replication 

Replication provides redundancy and increases data availability. With multiple copies of data on different database servers, replication protects a database from the loss of a single server. Replication also allows you to recover from hardware failure and service interruptions. With additional copies of the data, you can dedicate one to disaster recovery, reporting, or backup. 

In some cases, you can use replication to increase read capacity. Clients have the ability to send read and write operations to different servers. You can also maintain copies in different data centers to increase the locality and availability of data for distributed applications. 

