The added candidate disk device is not visible from all the nodes:ORA-15014: path '/dev/rASM' is not in the discovery set

when you add disk in asm diskgroup got error

Check in ASM alert log

SQL> Alter diskgroup DATA_HR add disk '/dev/rASM_PTT_001' ;
NOTE: GroupBlock outside rolling migration privileged region
ORA-15032: not all alterations performed
ORA-15031: disk specification '/dev/rASM_HR_001' matches no disks
ORA-15014: path '/dev/rASM_HR_001' is not in the discovery set
ERROR: Alter diskgroup DATA_HR add disk '/dev/rASM_HR_001'


If get error
Login as grid user

$sqlplus sys as sysasm

show parameter asm_diskstring

Alter system set asm_diskstring='/dev/rhdisk*', '/dev/rASM*'  scope=Both;



Here we have two type asm disk you can add more:-
/dev/rhdisk*', '/dev/rASM*'

Alter diskgroup DATA_HR add disk '/dev/rASM_PTT_001' ;

ref:
OERR: ORA-15014 "path '%s' is not in the discovery set" (varies by version) Reference Note ( Doc ID 194391.1 )
1389618.1 - Default Disk Discovery Path by Platform

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The ASM_DISKSTRING initialization parameter specifies a comma-delimited list of strings that limits the set of disks that an Oracle ASM instance discovers.
The discovery strings can include wildcard characters. Only disks that match one of the strings are    discovered.
The same disk cannot be discovered twice.