Add Shards to a Cluster¶
In production environments, all shards should be replica sets.
When you add a shard to a sharded cluster, you affect the balance of chunks among the shards of a cluster for all existing sharded collections. The balancer will begin migrating chunks so that the cluster will achieve balance. See Sharded Collection Balancing for more information.
Changed in version 2.6: Chunk migrations can have an impact on disk space. Starting in MongoDB 2.6, the source shard automatically archives the migrated documents by default. For details, see moveChunk directory.
When adding a shard to a cluster, always ensure that the cluster has enough capacity to support the migration required for balancing the cluster without affecting legitimate production traffic.
Add a Shard to a Cluster¶
You interact with a sharded cluster by connecting to a mongos instance.
mongo --host mongos0.example.net --port 27017
Add a shard to the cluster using the sh.addShard() method, as shown in the examples below. Issue sh.addShard() separately for each shard. If the shard is a replica set, specify the name of the replica set and specify a member of the set. In production deployments, all shards should be replica sets.
You can instead use the addShard database command, which lets you specify a name and maximum size for the shard. If you do not specify these, MongoDB automatically assigns a name and maximum size. To use the database command, see addShard.
The following are examples of adding a shard with sh.addShard():
To add a shard for a replica set named rs1 with a member running on port 27017 on mongodb0.example.net, issue the following command:
sh.addShard( "rs1/mongodb0.example.net:27017" )
To add a shard for a standalone mongod on port 27017 of mongodb0.example.net, issue the following command:
sh.addShard( "mongodb0.example.net:27017" )
It might take some time for chunks to migrate to the new shard.