undo_tablespace

Hello,

i'm trying to drop/create a new undo_tablespace at my oracle db version 12.1.0 by following the below command

***********************************************************************

sqlplus / as sysdba

CREATE UNDO TABLESPACE UNDOTBS2; 

alter system set undo_tablespace='UNDOTBS2' scope=BOTH;

DROP TABLESPACE UNDOTBS1 INCLUDING CONTENTS AND DATAFILES;

show parameter undo

NAME                 TYPE    VALUE

------------------------------------ ----------- ------------------------------

_gc_undo_affinity          boolean   FALSE

temp_undo_enabled          boolean   FALSE

undo_management           string   AUTO

undo_retention            integer   900

undo_tablespace           string   UNDOTBS2

==> till now everything is fine

now i restarted the database and immediately check show parameter undo

==>i noticed that it returned back to UNDOTBS1

SQL> show parameter undo