11gR2: PARALLELISM AUTO DOP / CALIBRATE IO / num_physical_disks and max_latency ?

Hi,I want to use AUTO DOP (Degree Of Parallelism) for the first time in database 11.2.3.0 to optimize queries such as :MERGE INTO PRODUCTS P USING (SELECT /*+ PARALLEL */ …              FROM (SELECT /*+ PARALLEL */…           WHERE DMP.no_partition = 894ON (P.col1 = D.col2)WHEN MATCHED THEN  UPDATE … ALTER SYSTEM SET parallel_degree_policy=LIMITED; ALTER SESSION SET PARALLEL_DEGREE_LIMIT= 4 ; -- To have degree cappedBut I have also to execute DBMS_RESOURCE_MANAGER.CALIBRATE_IO to populate IO statistics.select * from v$io_calibration_status; no rows selected ; DBMS_RESOURCE_MANAGER.CALIBRATE_IO ( num_physical_disks IN PLS_INTEGER DEFAULT 1,max_latency IN PLS_INTEGER DEFAULT 20,