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export ORACLE_SID=+ASM
sqlplus / as sysdba

Startup and Shutdown of ASM Instances

ASM instance are started and stopped in a similar way to normal database instances. The options for the STARTUP command are:

• FORCE – Performs a SHUTDOWN ABORT before restarting the ASM instance.
• MOUNT – Starts the ASM instance and mounts the disk groups specified by the ASM_DISKGROUPS parameter.
• NOMOUNT – Starts the ASM instance without mounting any disk groups.
• OPEN – This is not a valid option for an ASM instance.

The options for the SHUTDOWN command are:

• NORMAL – The ASM instance waits for all connected ASM instances and SQL sessions to exit then shuts down.
• IMMEDIATE – The ASM instance waits for any SQL transactions to complete then shuts down. It doesn’t wait for sessions to exit.
• TRANSACTIONAL – Same as IMMEDIATE.
• ABORT – The ASM instance shuts down instantly.

ASM Disk Groups

  level of redundancy:

• NORMAL REDUNDANCY – Two-way mirroring, requiring two failure groups.
• HIGH REDUNDANCY – Three-way mirroring, requiring three failure groups.
• EXTERNAL REDUNDANCY – No mirroring for disks that are already protected using hardware mirroring or RAID. If you have hardware RAID it should be used in preference to ASM redundancy, so this will be the standard option for most installations.

Create Example : 

CREATE DISKGROUP disk_group_1 NORMAL REDUNDANCY
  FAILGROUP failure_group_1 DISK
    '/devices/diska1' NAME diska1,
    '/devices/diska2' NAME diska2
  FAILGROUP failure_group_2 DISK
    '/devices/diskb1' NAME diskb1,
    '/devices/diskb2' NAME diskb2;

DROP Example : 

DROP DISKGROUP disk_group_1 INCLUDING CONTENTS;

Using Alter to Add Disk : 

ALTER DISKGROUP disk_group_1 ADD DISK
  '/devices/disk*3',
  '/devices/disk*4';

Using Alter to Drop Disk :

ALTER DISKGROUP disk_group_1 DROP DISK diska2;

Using Alter to Re-size Disk : 

ALTER DISKGROUP disk_group_1
  RESIZE DISK diska1 SIZE 100G;

 Using Alter to Re-size all disk in Failure Group:

ALTER DISKGROUP disk_group_1
  RESIZE DISKS IN FAILGROUP failure_group_1 SIZE 100G;

 Using Alter to Resize all Disk In DiskGroup :

ALTER DISKGROUP disk_group_1
  RESIZE ALL SIZE 100G;

Using Alter To dismiss pending disk to be Dropped :

ALTER DISKGROUP disk_group_1 UNDROP DISKS;

 Some Useful Command to Mount ASM disk group Manually : 

ALTER DISKGROUP ALL DISMOUNT;
ALTER DISKGROUP ALL MOUNT;
ALTER DISKGROUP disk_group_1 DISMOUNT;
ALTER DISKGROUP disk_group_1 MOUNT;

 Thank You 

Osama mustafa