Here are ASM best practices to add disks which should be always used to manipulate the ASM disks
(1) First check the newly added disk is visible in ASM disks
select header_status,path from v$asm_disk where path= '<path>';
It should show the candidate
(2) Create a new temporary diskgroup using those disks
CREATE DISKGROUP TEST_DISK EXTERNAL REDUNDANCY DISK '<path>';
(3) Check if the diskgroup is created and mounted
SELECT STATE, NAME FROM V$ASM_DISKGROUP;
(4) If RAC, then manually mount it on the other ASM instance(s)
ALTER DISKGROUP TEST_DISK MOUNT;
SELECT STATE, NAME FROM V$ASM_DISKGROUP;
(5) If the previous steps had success and the TEST diskgroup can be successfully mounted (on each ASM instance), then drop the TEST_DISK diskgroup as follow
alter diskgroup test_disk dismount; (from all the ASM instances, except from one).
DROP DISKGROUP TEST; --(from the ASM instance, which the diskgroup is still mounted)
(6) Now again check the status of the disk
select header_status,path from v$asm_disk where path= '<path>';
It should show Former
(7) Then the candidate disk is ready to be added to the desired diskgroup:
ALTER DISKGROUP ADD DISK '<path>';
(8) Check the rebalance in ASM using
select * from v$asm_operation;
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