Oracle RAC - ASM Disks and Diskgroups - (Create, Drop and Alter ASM disk groups)

Create, Drop and Alter ASM disk groups

Create Disk Group:
Create Disk groups using the CREATE DISKGROUP statement and specify the level of redundancy. 

Disk group redundancy types:-
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 RAID or mirroring.

SQL> CREATE DISKGROUP data NORMAL REDUNDANCY
FAILGROUP failure_group_1 DISK '/dev/sda1' NAME dataa1,'/dev/sda2' NAME dataa2, 
FAILGROUP failure_group_2 DISK '/dev/sdb1' NAME datab1,'/dev/sdb2' NAME datab2;

Drop Disk Group:
Drop disk group using DROP DISKGROUP statement.
SQL> DROP DISKGROUP data INCLUDING CONTENTS;

Alter Disk Group:
Add or remove disks from disk groups Using ALTER DISKGROUP statement. You can also use wildcard "*" to reference disks.

Add a disk.
SQL> ALTER DISKGROUP data ADD DISK '/dev/datac1', '/dev/datac2';

Add all reference disks
SQL> ALTER DISKGROUP data ADD DISK '/dev/datad*;

Drop/remove a disk.
SQL> ALTER DISKGROUP data DROP DISK datab2;

The UNDROP command used to undo only pending drop of disks. After you drop the disks you cannot revert.
SQL> ALTER DISKGROUP data UNDROP DISKS;

Diskgroup Rebalance:
Disk groups can be rebalanced manually Using REBALANCE clause and you can modify the POWER clause default value. 
SQL> ALTER DISKGROUP disk_group_1 REBALANCE POWER 5;

MOUNT and DISMOUNT DiskGroups:
Normally Disk groups are mounted at ASM instance startup and dismounted at shutdown. Using MOUNT and DISMOUNT options you can make one or more Disk Groups available or unavailable. 
SQL> ALTER DISKGROUP data MOUNT;
SQL> ALTER DISKGROUP data DISMOUNT;
SQL> ALTER DISKGROUP ALL MOUNT;
SQL> ALTER DISKGROUP ALL DISMOUNT;

DiskGroup Check:
Use CHECK ALL to verify the internal consistency of disk group metadata and repair in case of any error. 
SQL> ALTER DISKGROUP data CHECK ALL;

DiskGroup resize:
Resize the one or all disks in the Diskgroup. 

Resize all disks in a failure group.
SQL> ALTER DISKGROUP data RESIZE DISKS IN FAILGROUP failure_group_1 SIZE 1024G;

Resize a specific disk.
SQL> ALTER DISKGROUP data RESIZE DISK dataa1 SIZE 1024G;

Resize all disks in a disk group.
SQL> ALTER DISKGROUP data RESIZE ALL SIZE 1024G;

--------------------------------------------------------------------------------------------------------------------------------------------