How to add disk in ASM diskgroup

Below are three important Diskgroup types you must know before adding disk:

MEMBER – Disk is a member of an existing disk group.
FORMER РDisk was once part of a disk group but has been dropped cleanly from the group. It may be added to a new disk group with the ALTER DISKGROUP statement.
CANDIDATE – Disk is not part of a disk group and may be added to a disk group with the ALTER DISKGROUP statement.

To add disk into ASM it should be “CANDIDATE disk” or “FORMER disk”.

Steps to add disk in diskgroup:

Login into asm--->

$ sqlplus /as sysasm

SQL> col path for a25;
col name for a20;
select header_status,name,path,free_mb,CREATE_DATE from v$asm_disk;

Check if any candidate disk is present by above command if present fire below command to add disk, if Candidate disk or Former disk is not there then you have to take follow up with storage team and need to raise request for storage.

SQL>ALTER DISKGROUP DG1 ADD DISK '/dev/mapper/asm_disk50' REBALANCE POWER 11;

You disk has been added successfully ...

 

Below is explanation of Rebalance Power:

What is Rebalance Power in ASM?
If we add or remove disk from Diskgroup data gets rebalanced into others disks with the rebalance power.
Higher number means rebalancing operation will complete faster but it will consume more IO and lower 
number means rebalancing operation will take longer but less IO.
Power 11 = do stuff faster than power 6 (consume more I/O and CPU) 

Example:
In below example the rebalance of disk21 would wait until disk22 rebalance completes.
alter diskgroup name1 add disk '/dev/asm_disk21' rebalance power 6;
alter diskgroup name2 add disk '/dev/asm_disk22' rebalance power 11;
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