SQL> conn / as sysdba
Connected.
SQL> select group_number,disk_number,name,path from v$asm_disk where group_number=3;

GROUP_NUMBER DISK_NUMBER NAME PATH
------------ ----------- ------------------------------ ------------------------------
3 0 FRA_0000 /dev/rdisk/disk27
3 1 FRA_0001 /dev/rdisk/disk28

SQL>
SQL> alter diskgroup fra drop disk fra_0001;
alter diskgroup fra drop disk fra_0001
*
ERROR at line 1:
ORA-15032: not all alterations performed
ORA-15260: permission denied on ASM disk group

使用sysdba登录执行alter diskgroup会提示没有权限。
执行alter diskgroup操作，需要使用sysasm登录。

SQL> conn / as sysasm
Connected.
SQL> alter diskgroup fra drop disk fra_0001;