Docs Menu
Docs Home
MongoDB Manual
/ / /


On this page

  • Definition
  • Considerations
  • Examples

Adds a shard replica set to a sharded cluster.


In mongosh, this command can also be run through the sh.addShard() helper method.

Helper methods are convenient for mongosh users, but they may not return the same level of information as database commands. In cases where the convenience is not needed or the additional return fields are required, use the database command.

Run addShard when connected to a mongos instance. The command takes the following form to add a shard replica set:

{ addShard: "<replica_set>/<hostname><:port>", maxSize: <size>, name: "<shard_name>" }

The command contains the following fields:


The replica set name, hostname, and port of at least one member of the shard's replica set. Any additional replica set member hostnames must be comma separated. For example:

<replica_set>/<hostname><:port>,<hostname><:port>, ...
Optional. The maximum size in megabytes of the shard. If you set maxSize to 0, MongoDB does not limit the size of the shard.
Optional. A name for the shard. If this is not specified, MongoDB automatically provides a unique name.

The addShard command stores shard configuration information in the config database. Always run addShard when using the admin database.

Specify a maxSize when you have machines with different disk capacities, or if you want to limit the amount of data on some shards. The maxSize constraint prevents the balancer from migrating chunks to the shard when the totalSize returned from running listDatabases on the shard exceeds the value of maxSize.

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 Cluster Balancer for more information.

Chunk migrations can have an impact on disk space, as the source shard automatically archives the migrated documents by default. For details, see moveChunk directory.


You cannot include a hidden member in the seed list provided to addShard.

The following command adds a replica set as a shard:

use admin
db.runCommand( { addShard: "repl0/"} )


Do not use localhost for the hostname unless your config server is also running on localhost.