HOW TO RECREATE ASM INSTANCES AND DISKGROUPS, if ASM INSTANCE or DGroups Currepted

RECREATING ASM INSTANCES AND DISKGROUPS
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In the event you cannot mount your ASM disk groups, you will be unable to start
any databases using those disk groups.  Here is a possible error reported when
mounting ASM disk groups:

SQL> startup mount

ORA-15032: not all alterations performed
ORA-15063: diskgroup "" lacks quorum of 2 PST disks; 0 found

This error may occur if:

a) ASM disk(s) is not visible on the operating system.
b) asm_diskstring parameter is not set correctly on ASM instance(s)
c) ASM metadata in disk is overwritten or corrupted

If you have seen this error or another error indicating ASM metadata corruption
and have verified that the disk(s) is visable with correct permissions on the
operating system and that the asm_diskstring parameter is set correctly, your
ASM metadata may be corrupted.  If this is the case, you may need to re-create
your ASM instance(s) and disk group(s).  The steps are:

1. Ensure that you have a prior RMAN backup of all databases using ASM
2. Shut down your ASM instance(s)
3. Use dd to clear the metadata from ASM disks
4. Re-create your ASM disk group(s)
5. Restore databases


STEP 1: ENSURE THAT YOU HAVE A PRIOR RMAN BACKUP OF ALL DATABASES USING ASM
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The only way you can recover from ASM metadata corruption is to have a prior
RMAN backup of the database in an area that would not be affected by an ASM
instance outage.  As part of your recovery strategy, you should consider
integrating tape or other tertiary storage to safeguard your backups.

Example of RMAN backup:

1. Connect RMAN to the target database for backup

  rman nocatalog target /

2. Now Backup your Database, Archive logs and Control files.  Example:

  RMAN> backup device type disk format '/u03/backup/%U' database plus archivelog;
  RMAN> backup device type disk format '/u03/backup/ctrlf_%U' current controlfile;

3. Manually make copies of your spfiles.  Example:

  CREATE PFILE='/u03/app/oracle/product/10.1.0/dbs/init.ora'
  FROM SPFILE='/+DATA/V10FJ/spfile.ora';

If you do not have a good backup of all databases (datafiles, controlfiles,
redo logs, archive logs), DO NOT CONTINUE BEYOND STEP 1!


STEP 2: SHUT DOWN YOUR ASM INSTANCE(S)
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Stop your database instances and ASM instances with sqlplus or srvctl (RAC)

SQLPLUS Example:

  setenv ORACLE_SID +ASM
  sqlplus '/ as sysdba'
  SQL> shutdown immediate

  setenv ORACLE_SID DBSCOTT
  sqlplus '/ as sysdba'
  SQL> shutdown immediate

SRVCTL (RAC) Example:

  srvctl stop asm -n
  srvctl stop asm -n
  srvctl stop database -d


STEP 3: USE DD TO CLEAR THE METADATA FROM ASM DISKS
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All ASM metadata must be cleared before attempting to re-create ASM instances
and diskgroups.  Example Command:

  dd if=/dev/zero of=/dev/rdsk/c1t4d0s4 bs=8192 count=12800


STEP 4: RE-CREATE YOUR ASM DISK GROUP(S)
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Set your ORACLE_SID to your ASM instance and create a new diskgroup.  Example:

  setenv ORACLE_SID +ASM
  sqlplus '/ as sysdba'
  SQL> startup nomount
  SQL> create diskgroup data disk '/dev/rdsk/c1t4d0s4';
  SQL> shutdown immediate
  SQL> startup mount


STEP 5: RESTORE DATABASES
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1. Start instance using the local copy of your pfile from step 1.

  setenv ORACLE_SID DBSCOTT
  sqlplus '/ as sysdba'
  SQL> startup nomount pfile=init.ora

2. Use RMAN to restore the controlfiles and database.  Example:

  rman target /
  RMAN> restore controlfile from '/u03/backup/ctrlf_'; -- where  is the unique string generated by %U.
  RMAN> alter database mount;
  RMAN> restore database;
  RMAN> recover database;
  RMAN> alter database open resetlogs;

3. Connect to the ASM instance and get the controlfile name.  Example:

  setenv ORACLE_SID +ASM
  sqlplus '/ as sysdba'
  SQL> select name, alias_directory from v$asm_alias;

  Look for the controlfile name under the CONTROLFILE directory eg: Current.256.1

4. Edit the init.ora and change the control_files parameter to point to
   the one identified from the ASM v$asm_alias view.

5. Re-create the spfile.  Example:

  SQL> create spfile='+DATA/V10FJ/spfileV10FJ.ora'
       from pfile='/u03/app/oracle/product/10.1.0/dbs/pfile.out';

6. Shutdown and restart the instance to use the newly created spfile.

7. Repeart the "STEP 5" section for additional databases.