ASM: adding diskgroup

SQL> alter diskgroup data add disk '/dev/raw/raw2' size 1019m;
alter diskgroup data add disk '/dev/raw/raw2' size 1019m
*
ERROR at line 1:
ORA-15032: not all alterations performed
ORA-15033: disk '/dev/raw/raw2' belongs to diskgroup "DATA"

SQL> a force
1* alter diskgroup data add disk '/dev/raw/raw2' size 1019m force
SQL> /

Diskgroup altered.