ASM disks

Here is using Oracle 12.2 , 2 nodes configuration on AIX , I have a disk group with 2 disks form normal redundancy

with reference to Doc ID 443835.1,

I tried to simulate disk lost. but situation is when I change one of the disk permission for example /dev/rhdiskasm1 to root.system, (original oracle.dba)

the disk group dismount automatically.

I saw there is error in the asm alert log

2018-01-11T11:17:06.680215+08:00

NOTE: process _user32309442_+asm1 (32309442) initiating offline of disk 2.3105232822 (DISKASM3) with mask 0x7e in group 2 (DGTEST) with client assisting

NOTE: checking PST: grp = 2

2018-01-11T11:17:06.686354+08:00

GMON checking disk modes for group 2 at 34 for pid 35, osid 32309442