I suggest to verify the installation log to see what was used to create the disk group. Once a disk group has been created, the AU size cannot be altered. Also, please tell your OS version or distribution and exact Oracle ASM version you are using.
I verified the installation log file , I found follow command for creating ASM instance and diskgroup
/u01/app/11.2.0/grid/bin/asmca -silent -oui_internal -configureASM -diskString '/dev/oracleasm/disks/*' -diskGroupName DATA -diskList /dev/oracleasm/disks/SDB1,/dev/oracleasm/disks/SDC1 -redundancy EXTERNAL
It shows that Grid Infrastructure Installation Software doesn't set AU size (I expect it has "-au_size 4" parameter but it hasn't)
do you think it's a bug ?
the oracle version is 22.214.171.124
and OS is Oracle EL6 64 bit
According to the info it's bug 14009493 , ID 1517960.1, which ignores the au_size value specified via oui.
It's apparently fixed in 126.96.36.199.