Archivelog redundancy
You can use ALTERNATE attribute in second archive log destination.


  ALTERNATE
  
  Specifies an alternate archiving destination to be used when the original destination fails.


Example:

LOG_ARCHIVE_DEST_1='LOCATION=/disk1 MANDATORY ALTERNATE=LOG_ARCHIVE_DEST_2'
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_2='LOCATION=/disk2 MANDATORY'
LOG_ARCHIVE_DEST_STATE_2=ALTERNATE


Reference:
LOG_ARCHIVE_DEST_n Parameter Attributes