How to Get All Oracle Databases Size From OEM Repository

Database Manager asks you as a DBA about all the database size in the supported environment .

SQL> select host_name,target_name, sum( FILE_SIZE/1024/1024/1024)
     from mgmt$db_datafiles 
     group by host_name,target_name 
     order by host_name, target_name;

HOST_NAME                                TARGET_NAME                              SUM(FILE_SIZE/1024/1024/1024)
---------------------------------------- ---------------------------------------- -----------------------------
HOST1                                    DB1                                                    38.65
HOST2                                    DB2                                                    385.88
HOST3                                    DB3                                                    27.52

OR we can use another another view mgmt$db_tablespaces :

SQL> select host_name,target_name,sum( TABLESPACE_SIZE/1024/1024/1024) 
     from mgmt$db_tablespaces 
     group by host_name,target_name 
     order by 1,2;