You can add a container to an SMS table space only on a database partition that currently has no containers.
ALTER TABLESPACE name
ADD ('path')
ON DBPARTITIONNUM (database_partition_number)
The database partition specified by number, and every partition in the range of database partitions, must exist in the database partition group on which the table space is defined. A database_partition_number might only appear explicitly or within a range in exactly one db-partitions-clause for the statement.
ALTER TABLESPACE plans
ADD ('/dev/rhdisk0')
ON DBPARTITIONNUM (3)