scaling current cluster

[Erez Zarum]

I have 3 shards, each shard consist of a 3 replicaset nodes.

I plan to scale it by adding another 2 shards (each one has 3 nodes as well)

As this is not documented, i understand that i have to first create 2 different replicaset configurations (As i would normally create in a non sharded environment for HA), then add those 2 replicasets into the cluster (sh.addshard)?

My total shard size is around 7TB (over 3 shards), which impact i might expect to get on my cluster after introducing those 2 new shards? are there any other things i should be aware of? excessive disk space during balance? (except those in the moveChunk directory)

[David Hows]

Hi Erez,

You may want to look at this page in the mongodb docs - http://docs.mongodb.org/manual/tutorial/add-shards-to-shard-cluster/

Regarding your questions

As this is not documented, i understand that i have to first create 2 different replicaset configurations (As i would normally create in a non sharded environment for HA), then add those 2 replicasets into the cluster (sh.addshard)?

Correct, you add these just like you added the original three replica sets.

My total shard size is around 7TB (over 3 shards), which impact i might expect to get on my cluster after introducing those 2 new shards? are there any other things i should be 

aware of? excessive disk space during balance? (except those in the moveChunk directory)

Currently mongo does not automatically reclaim disk space as part of deletions. So you can expect to see your disk usage increase as chunk migrations occur. Additionally, when adding new shards there can be some performance impacts as a large number of shards are moved. 

Cheers,

David