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In sharding when a node goes down, the data stored in the node will be lost. So it provides only a limited fault tolerance to the system. Sharding and replication can be combined to make the system fault tolerant and highly available. Figure 2.11 illustrates the combination of sharding and replication where the data set is split up into shard A and shard B. Shard A is replicated across node A and node B; similarly shard B is replicated across node C and node D.

Figure 2.10 Peer‐to‐peer model.

Figure 2.11 Combination of sharding and replication.