Drop last active Diskgroup in Oracle 11g ASM

This document will describe how to drop the last active Diskgroup in Oracle 11g ASM.
In my testing virtual box i installed standalone Grid 11g with ASM on Oracle Linux 6.4
i simulated the scenario to drop the last active disk group.

First tried to drop the last active diskgroup, Oracle thrown  the error like below.

SQL> drop diskgroup data including contents;
drop diskgroup data including contents
*
ERROR at line 1:
ORA-15039: diskgroup not dropped
ORA-15027: active use of diskgroup "DATA" precludes its dismount


Solution:- dismount the active diskdroup with force.

SQL> alter diskgroup data dismount force;

Diskgroup altered.

Drop the dismounted diskdroup using force.

SQL> drop diskgroup data force including contents;

Diskgroup dropped.

Verify  the diskgroups.

SQL> select * from V$ASM_DISKGROUP;

no rows selected