ORA-15410: Disks in disk group DISKGROUP_NAME do not have equal size

If you are trying to create a diskgroup (suppose diskgroup name is DATA) and you see errors as bellow

ORA-15018: diskgroup cannot be created ORA-15410: Disks in disk group DATA do not have equal size

following would be the reason of it.

Starting Grid Infrastructure 12.1.0.2, we need to have all disks with same size in a disk group, unlike previous versions where we could have varying sized disks in a diskgroup. So if we face ORA-15410 while creating a diskgroup, it would mean that disk size(s) is/are different in the diskgroup; which you are creating. Make sure that all disks being used in this disk group have same size and try again.