Following step by step guide will help you to add disk to oracle ASM diskgroup.

// Following query will identify the Diskgroup to add disk:

SQL> select group_number, name from v$asm_diskgroup;
GROUP_NUMBER NAME
------------ ------------------------------
1 DATA

// Following query will identify the candidate disk:

SQL> SELECT MOUNT_STATUS,HEADER_STATUS,MODE_STATUS,STATE,TOTAL_MB,FREE_MB,NAME,PATH,LABEL FROM V$ASM_DISK;

MOUNT_S HEADER_STATU MODE_ST STATE TOTAL_MB FREE_MB NAME PATH LABEL
------- ------------ ------- -------- ---------- ---------- ------------------------------ ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -------------------------------
CACHED MEMBER ONLINE NORMAL 10240 6528 DATA_0002 /dev/oracleasm/disks/OCR
CACHED MEMBER ONLINE NORMAL 307200 196112 DATA_0000 /dev/oracleasm/disks/ARCHIVE
CACHED MEMBER ONLINE NORMAL 307200 196141 DATA_0001 /dev/oracleasm/disks/DATA

// With the help of createdisk oracle utility, we will create oracle ASM disk. ( as root user ) Following command will create ASM disk:

[root@database1 ~]# /usr/sbin/oracleasm createdisk RMAN /dev/mapper/mpathg
Writing disk header: done
Instantiating disk: done

Note:
RMAN is the name of newly created ASM disk with path ‘/dev/mapper/mpathg’.

// Scan all oracle ASM disk after addition:

[root@database1 ~]# /usr/sbin/oracleasm scandisks
Reloading disk partitions: done
Cleaning any stale ASM disks...
Scanning system for ASM disks...

// Ensure all oracle ASM disk after scanning as follow:

[root@database1 ~]# /usr/sbin/oracleasm listdisks
ARCHIVE
DATA
OCR
 RMAN

OR

[oracle@database1 ~]$ cd /dev/oracleasm/disks/
[oracle@database1 disks]$ ls
ARCHIVE DATA OCR RMAN

// Now Add the newly created oracle ASM disk to existing ASM diskgroup with the help of following query:

[oracle@database1 disks]$ grid_env
[oracle@database1 disks]$ sqlplus "/ as sysasm"

SQL> ALTER DISKGROUP DATA ADD DISK '/dev/oracleasm/disks/RMAN' NAME DATA_0003 REBALANCE POWER 11;

Diskgroup altered.

// Ensure changes by issue following query:

SQL> SELECT MOUNT_STATUS,HEADER_STATUS,MODE_STATUS,STATE,TOTAL_MB,FREE_MB,NAME,PATH,LABEL FROM V$ASM_DISK;
MOUNT_S HEADER_STATU MODE_ST STATE TOTAL_MB FREE_MB NAME PATH LABEL
------- ------------ ------- -------- ---------- ---------- ------------------------------ ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -------------------------------
CACHED MEMBER ONLINE NORMAL 307200 202544 DATA_0000 /dev/oracleasm/disks/ARCHIVE
CACHED MEMBER ONLINE NORMAL 10240 6743 DATA_0002 /dev/oracleasm/disks/OCR
CACHED MEMBER ONLINE NORMAL 307200 202578 DATA_0001 /dev/oracleasm/disks/DATA
CACHED MEMBER ONLINE NORMAL 307200 292732 DATA_0003 /dev/oracleasm/disks/RMAN

By above method, we can add disk to oracle ASM diskgroup.

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Note: Please don’t hesitate to revert in case of any query OR feedback.

Thanking you.

Have a nice time. 🙂