How to add a new brick to an existing replicated volume?

Issue

• Adding a brick fails:

  # gluster vol add-brick test-volume-replicated3 host:/rhss/bricks/brick1/test-volume-replicated3
  volume add-brick: failed: Incorrect number of bricks supplied 1 with count 2
  

• Creating a 3-copy replica works:

  # gluster vol create test-volume-replicated3 replica 3 host1:/rhss/bricks/brick1/test-volume-replicated3 host2:/rhss/bricks/brick1/test-volume-replicated3 host3:/rhss/bricks/brick1/test-volume-replicated3
  volume create: test-volume-replicated3: success: please start the volume to access data
  # gluster vol info test-volume-replicated3
  
  Volume Name: test-volume-replicated3
  Type: Replicate
  Volume ID: 10b3d0e2-14a2-4ec3-a98c-9a3307f3fd8f
  Status: Created
  Number of Bricks: 1 x 3 = 3
  Transport-type: tcp
  Bricks:
  Brick1: host1:/rhss/bricks/brick1/test-volume-replicated3
  Brick2: host2:/rhss/bricks/brick1/test-volume-replicated3
  Brick3: host3:/rhss/bricks/brick1/test-volume-replicated3