From the perspective of a client application, whether a MongoDB instance is running as a single server (i.e. "standalone") or a replica set is transparent. 从客户端应用程序的角度来看，MongoDB实例是作为单个服务器（即“独立”）运行还是作为副本集运行是透明的。However, MongoDB provides additional read and write configurations for replica sets.但是，MongoDB为副本集提供了额外的读写配置。
Note注意
Sharded clusters where the shards are also replica sets provide the same operational semantics with regards to write and read operations.分片也是副本集的分片集群提供了与写入和读取操作相同的操作语义。
Read preference specifies where (i.e. which members of the replica set) the drivers should direct the read operations.读取首选项指定驱动程序应该在哪里（即副本集的哪些成员）引导读取操作。