In Oracle 12.2 an archive log directory is accepted, if top level directory does not exist:
[email protected]:/u01/app/oracle/product/12.2.0/dbhome_1/dbs/ [DMK] ls -l /u02/oradata/DMK/
total 2267920
drwxr-xr-x. 2 oracle dba        96 Dec  6 05:36 arch ...

Now database accepts this non existing archivelog destination:
SQL> alter system set log_archive_dest_3='LOCATION=/u02/oradata/DMK/arch/arch2';
System altered.

But not this:
SQL> alter system set log_archive_dest_4='LOCATION=/u02/oradata/DMK/arch/arch2/arch4';
alter system set log_archive_dest_4='LOCATION=/u02/oradata/DMK/arch/arch2/arch4'
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-16032: parameter LOG_ARCHIVE_DEST_4 destination string cannot be translated
ORA-07286: sksagdi: cannot obtain device information.
Linux-x86_64 Error: 2: No such file or directory

Log file format is set as following:
SQL> show parameter log_archive_format;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
log_archive_format                   string      %t_%s_%r.dbf


Now let’s see how archive log files look like in log_archive_dest_3:
[email protected]:/u01/app/oracle/product/12.2.0/dbhome_1/dbs/ [DMK] ls -l /u02/oradata/DMK/arch/arch2*
-rw-r-----. 1 oracle dba 3845120 Dec  6 05:36 /u02/oradata/DMK/arch/arch21_5_960106002.dbf

So Oracle just adds the non existing top level directory to beginning of archivelog filename.

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Oracle Team