Change ASM disk group from normal redundancy to external redundancy

Hello,

When the disk group was created with normal redundancy, the only way to change is to drop the disk group and recreate a new one.
Warning: If you drop disk group your data will be lost.
1) shutdown database

shutdown immediate;

2) startup in mount mode

startup mount;

3) make database full backup, archivelog backup, spfile backup and controlfile backup

RMAN> backup device type disk format '/u02/backup/backup/database_backup%U' database;

RMAN> backup device type disk format '/u02/backup/backup/archivelog%U' archivelog all;

SQL>  create pfile='/u02/backup/initorcl.ora' from spfile;

SQL>  alter database backup controlfile to '/u02/backup/control.ctl';

4) shutdown database;

shutdown immediate;

5) login as sysasm and drop disk group

[oracle@oel6 backup]$ . oraenv
ORACLE_SID = [orcl] ? +ASM
sqlplus / as sysasm

SQL> drop diskgroup DISKS including contents;

SQL> shutdown immedaite;

SQL> startup nomount;

6) run asmca and create new disk group with external redundancy

SQL> select status from v$instance;

STATUS
------------
STARTED

7) ASM instance is already started, now we must restore database and all related files.

[oracle@oel6]$ . oraenv
ORACLE_SID = [+ASM] ? orcl
sqlplus / as sysdba

SQL> startup nomount pfile='/u02/backup/initorcl.ora';

SQL> create spfile='+DISKS' from pfile='/u02/backup/initorcl.ora';

SQL> !rman target /

RMAN> restore controlfile from '/u02/backup/control.ctl';

RMAN> alter database mount;

RMAN> restore database;

RMAN> recover database;

unable to find archived log
archived log thread=1 sequence=8
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of recover command at 09/25/2013 12:11:31
RMAN-06054: media recovery requesting unknown archived log for thread 1 with sequence 8 
and starting SCN of 21904164

While recovery it will give an error for archive log missing, this is expected we need to open the database with resetlogs as

RMAN> alter database open resetlogs;

8)
for using correct spfile:

ASMCMD> cp '/u0/app/oracle/product/11.2.0/dbhome_1/dbs/spfileorcl.ora' '+DISKS/ORCL/spfileorcl.ora' 

delete spfile from file system

rm -rf /u0/app/oracle/product/11.2.0/dbhome_1/dbs/spfileorcl.ora

edit /u0/app/oracle/product/11.2.0/dbhome_1/dbs/initorcl.ora, which must contains link to our spfile in disk group.

*.SPFILE='+DISKS/orcl/spfileorcl.ora'

that's all.