A little puzzle on RMAN of 'control_file_record_keep_time' and 'RETENTION POLICY TO RECOVERY WINDOW

Dear buddy:

    I am puzzle on RMAN of 'control_file_record_keep_time' and 'RETENTION POLICY TO RECOVERY WINDOW OF'

   (1)  if  control_file_record_keep_time =7,  does that means the control_file will keep recovery information only form 7 days ? if I want to recover older that 7 days ,it would failed right ?

   (2)  if   RETENTION POLICY TO RECOVERY WINDOW OF 7 DAY;   does that means RMAN keeps the recover information only for 7 days and  older that 7 days ,it would failed. right ?

  (3)  if  RETENTION POLICY TO REDUNDANCY 2;  does that means RMAN keeps 2 copys , right?  If so , does it necessary ?  if I set RETENTION POLICY TO REDUNDANCY 2　and not set  RETENTION POLICY TO RECOVERY WINDOW  in RMAN, the