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Replication is the process of creating copies of the same set of data across multiple servers. When a node crashes, the data stored in that node will be lost. Also, when a node is down for maintenance, the node will not be available until the maintenance process is over. To overcome these issues, the data block is copied across multiple nodes. This process is called data replication, and the copy of a block is called replica. Figure 2.7 shows data replication.

Replication makes the system fault tolerant since the data is not lost when an individual node fails as the data is redundant across the nodes. Replication increases the data availability as the same copy of data is available across multiple nodes. Figure 2.8 illustrates that the same data is replicated across node A, node B, and node C. Data replication is achieved through the master‐slave and peer‐peer models.

Figure 2.7 Replication.

Figure 2.8 Data replication.