Administering ASM Disk Groups

ASM simplifies the administration of oracle related files in disk groups which provides secure storage with striping and mirroring capabilities. All disks in an ASM disk group should be of same size and have similar performance characteristics. As per ASM best practices, two disk groups are recommended.

DATADG - spfile, control file, redo log member and datafiles.
FRADG   - control file, redo log member, archived logs, flashback logs, RMAN backups and Data Pump dump file sets.

When the Storage Administrator presents the LUNs to OS as disk devices, the DBA can create the ASM disk groups.

Connect to ASM instance.
$ sqlplus / as sysasm

SQL> set pages 200 lines 150
SQL> col path form a50
SQL> SELECT name, path, header_status, os_mb FROM v$asm_disk;

NAME    PATH                           HEADER_STATUS  OS_MB
-----------  ----------------------------      ---------------------------    ------------  
                /dev/rdsk/emcpower1a  CANDIDATE               17399
                /dev/rdsk/emcpower2a  CANDIDATE               17399
                /dev/rdsk/emcpower3a  CANDIDATE               17399
                /dev/rdsk/emcpower4a  CANDIDATE               17399
                /dev/rdsk/emcpower5a  FORMER                    34807
                /dev/rdsk/emcpower6a  CANDIDATE               34807


SQL> CREATE DISKGROUP datadg EXTERNAL REDUNDANCY
          DISK  '/dev/rdsk/emcpower1a', '/dev/rdsk/emcpower2a', '/dev/rdsk/emcpower3a';

SQL> SELECT name, path, header_status, os_mb FROM v$asm_disk;

NAME                    PATH                       HEADER_STATUS   OS_MB
----------------------    ----------------------------      ---------------------------   ----------------
 DATADG_0000   /dev/rdsk/emcpower1a  MEMBER                     17399  
 DATADG_0001   /dev/rdsk/emcpower2a  MEMBER                     17399
 DATADG_0002   /dev/rdsk/emcpower3a  MEMBER                     17399
                           /dev/rdsk/emcpower4a  CANDIDATE                 17399
                           /dev/rdsk/emcpower5a  FORMER                      34807
                           /dev/rdsk/emcpower6a  CANDIDATE                 34807

Add same size candidate disk to the disk group.
SQL> ALTER DISKGROUP datadg ADD DISK '/dev/rdsk/emcpower4a';

To drop the disk from disk group.
SQL> ALTER DISKGROUP datadg DROP DISK DATADG_0003;

SQL> SELECT operation, state, power, est_minutes FROM v$asm_operation;

OPERATION     STATE   POWER  EST_MINUTES
------------------      ----------   -----------     ---------------------
REBAL              DROP              1                     23

Watch the state of DATADG_0003 device as DROPPING and free_mb is changing with the time.
SQL> SELECT name, path, total_mb, free_mb, state FROM v$asm_disk;

Alternatively at command prompt.
$ asmcmd lsdg

ASM instance startup mounts the disk groups and shutdown unmounts those.
To manually mount and unmount the disk group(s).
SQL> ALTER DISKGROUP DATADG mount;
SQL> ALTER DISKGROUP DATADG dismount;
SQL> ALTER DISKGROUP ALL mount;
SQL> ALTER DISKGROUP ALL dismount;

To view disk group compatibility.
SQL> SELECT name, compatibility, database_compatibility FROM v$asm_diskgroup;