When you drop a disk group, you delete the disk group optionally with all of its files. You cannot drop a disk group if any of its database files are open. Oracle ASM deletes all of the disk group contents only if you specify the including contents option. After dropping a disk group, you can add its member disks to other disk groups or use them for other purposes.
One reason to drop a disk group is to change the redundancy level (normal, high, or external). Because you cannot change the redundancy of a disk group, you must drop the disk group and then re-create it with the proper redundancy. In this case, you must back up or move disk group data before you drop the disk group.
To drop a disk group:
Access the Oracle ASM home page.
See "Accessing the Oracle Automatic Storage Management Home Page" for instructions.
Click the Disk Group tab to display the Disk Groups page.
If the Oracle ASM Login page appears, log in as the SYS user, connecting as SYSASM. Provide the SYS password for the Oracle ASM instance. This password was set up when the Oracle ASM instance was created.
Click the box in the Select column to select a disk group that you plan to drop.
Click Delete and the confirmation page appears.
To delete the disk group even if it still contains files, click Show Advanced Options and ensure that the Including Contents option is selected. If the disk group contains files and the Including Contents option is not selected, then you cannot drop the disk group.
To delete a disk group that belongs to a disk group that you cannot mount, use the FORCE option in the Advanced Options confirmation dialog. The FORCE option applies to the DISMOUNTED disk group only. This option enables you to delete a disk header and mark it as FORMER.
On the confirmation page, click Yes.
For more information about dropping disks, see "Dropping Disk Groups".