Automatic Storage Management :: Disk Add  Query

Suppose i have created a diskgroup using

CREATE DISKGROUP disk_group_1 NORMAL REDUNDANCY
FAILGROUP failure_group_1 DISK
'/devices/diska1' NAME diska1,
'/devices/diska2' NAME diska2
FAILGROUP failure_group_2 DISK
'/devices/diskb1' NAME diskb1,
'/devices/diskb2' NAME diskb2;

now i want to add more disk in diskgroup then we can use

ALTER DISKGROUP disk_group_1 ADD DISK
'/devices/disk*3',

now my question is

(1) in which failgroup thE Disk*3 will be added ?
(2) How ican maintain eqal no of disk with same size availble in each FAILGROUP for data mirroring or redundancy by ASM ?