Identify existing disk groups and determine the free disk space that they contain. Optionally, identify failure groups for the Oracle ASM disk group devices.

If you intend to use a normal or high redundancy disk group, then you can further protect your database against hardware failure by associating a set of disk devices in a custom failure group. By default, each device comprises its own failure group. However, if two disk devices in a normal redundancy disk group are attached to the same Host Bus Adapter (HBA), then the disk group becomes unavailable if the adapter fails. The adapter in this example is a single point of failure.

To protect against failures of this type, you could use two HBAs, each with two disks, and define a failure group for the disks attached to each adapter. This configuration would enable the disk group to tolerate the failure of one HBA.