Duplicating a Database using RMAN
By Michael Ritacco, Oraclenotes.com

1. Run the script below on the database in which you plan to duplicate to generate the new paths for the data files. This example assumes you have enough disk space on one mount point. However, you can easily change some of the mount points in VI to point another location or modify the script to suit your specific needs.

   select 'set auxname for datafile ' || file# || ' to ' || '''/ora<XXX>/oradata/<SID>' ||
   substr(name, instr(name, '/', -1)) || ''';'
   from v$datafile
   /

2. Create the RMAN script to perform the duplicate. The number of log groups must match the source database. You may increase or decrease the number of log members as needed. You must also insert your auxname commands before the rman run block. If you are not doing a point in time dupilcate you can remove the optional line "set until time ...".
   
   

   ----------------------------------------------------------------------------------------------------------
   connect target sys/<password>@<sid>
   connect auxiliary /
   connect catalog rman/<password>@<sid>

   <Insert data file rename commands from step 1>

   run {
   -- Optional Line -- set until time '2001-12-18:08:30:00';
   allocate auxiliary channel a0 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a1 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a2 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a3 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a4 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a5 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a6 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a7 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a8 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a9 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a10 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a11 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a12 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a13 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a14 type <DISK/SBT_TAPE>;
   allocate auxiliary channel a15 type <DISK/SBT_TAPE>;
   duplicate target database to <NEW_SID>
   logfile
   group 1 ('/ora<XXX>/oradata/<SID>/redo01_01.rdo') size 200M reuse,
   group 2 ('/ora<XXX>/oradata/<SID>/redo02_01.rdo') size 200M reuse,
   group 3 ('/ora<XXX>/oradata/<SID>/redo03_01.rdo') size 200M reuse,
   group 4 ('/ora<XXX>/oradata/<SID>/redo04_01.rdo') size 200M reuse;
   }
   ----------------------------------------------------------------------------------------------------------

3. Log into the server where you will be duplicating the database.
   
   
4. If you are using RMAN duplicate to refresh a TEST or Development database first. Shutdown the instance if it already running.
   
   
5. You will need to recreate/create the password file on for the target database.
   You do not have to delete the data files of the existing database if one exists (applicable to only a refresh). It would be a good idea to do so if you are not sure that the source and the target you are duplicating too has the same name and number of data files. If not you will have unused data files on the duplicate database, wasting server resources.
   
   
6. STARTUP NOMOUNT the Target database.
   Note: You must have an adequately sized SORT_AREA_SIZE for RMAN to do its quering against the auxiliary database since it will not have any temp space available in NOMOUNT.
   
   
7. For the recovery part of the duplicate you will need the archive logs of the source database available. The archive logs can be copied over from the production machine to the target machine as long as the archive logs are placed in the exact path as on the production machine. Otherwise, you must do an archive log backup via Rman to either disk or tape. Remember that if you use a combination of Disk and Tape backups to allocate channels for both tape and disk in your script.
   
   
8. If you are doing a duplicate from a point in time you must set the NLS environmental variables. If not you can skip this step.
   
   C- Shell
   setenv NLS_LANG american
   setenv NLS_DATE_FORMAT YYYY-MM-DD:HH24:MI:SS

   Korn Shell
   export NLS_LANG= American
   export NLS_DATE_FORMAT= YYYY-MM-DD:HH24:MI:SS

9. Run the completed duplicate script
   $ rman @runscript

Note: If for any reason the duplicate fails due to missing archive log file or any other reason, it is still possible to finish the recovery manually, however the DBID will not be reset. Also, If you are duplicating a Multimaster replicated production database be sure to set job_queue_processes=0 to avoid pushing replication transactions to your production databases.

10. Make sure your global name is set correctly fro your target database because RMAN does not set this for you. It is also important to note that if you change the domain you must rebuild any database links.

    SQL> select * from global_name;
    SQL> alter database rename global_name to <new name>;

11. Remember to add any temporary files for any tablespaces that are using them.
12. Change any passwords for the new database.