LOG_ARCHIVE_DEST_n on 11gR2

On 11gR2, The LOG_ARCHIVE_DEST_n initialization parameter defines up to 31 (where n = 1, 2, 3, ... 31).

SQL> show parameter log_archive_dest_31

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_31 string

When created database by using dbca. I saw LOG_ARCHIVE_DEST_1 through LOG_ARCHIVE_DEST_9 be able to fill up. About LOG_ARCHIVE_DEST_10 (If DB_RECOVERY_FILE_DEST is specified and no LOG_ARCHIVE_DEST_n is specified, then LOG_ARCHIVE_DEST_10 is implicitly set to the recovery area. So can not see LOG_ARCHIVE_DEST_10), What about LOG_ARCHIVE_DEST_11 through LOG_ARCHIVE_DEST_31?

Then I checked from All Initialization Parameters page... I found LOG_ARCHIVE_DEST_n initialization parameter (where n = 1 - 10) be on Archive Category and LOG_ARCHIVE_DEST_n initialization parameter (where n = 11 - 31) be on Miscellaneous Category.

So. read more:
- If configured, each LOG_ARCHIVE_DEST_1 through LOG_ARCHIVE_DEST_10 destination must contain either a LOCATION or SERVICE attribute to specify a local disk directory or a remotely accessed database, respectively. Each LOG_ARCHIVE_DEST_11 through LOG_ARCHIVE_DEST_31 destination must contain a SERVICE attribute.
- LOG_ARCHIVE_DEST_11 through LOG_ARCHIVE_DEST_31 cannot be specified as an ALTERNATE redo transport location.
- LOG_ARCHIVE_DEST_11 through LOG_ARCHIVE_DEST_31 can only be used when the COMPATIBLE initialization parameter is set to 11.2.0.0 or later.

SQL> alter system set log_archive_dest_6='location=+disk02'

System altered.

SQL> alter system set log_archive_dest_11='location=+disk02'
alter system set log_archive_dest_11='location=+disk01'
*
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-16025: parameter LOG_ARCHIVE_DEST_11 contains repeated or conflicting attributes