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 SCSI controller, then the disk group becomes unavailable if the controller fails. The controller in this example is a single point of failure.
To protect against failures of this type, you could use two SCSI controllers, each with two disks, and define a failure group for the disks attached to each controller. This configuration would enable the disk group to tolerate the failure of one SCSI controller.
Note:If you define custom failure groups, then you must specify a minimum of two failure groups for normal redundancy and three failure groups for high redundancy.
See Also:Oracle Automatic Storage Management Administrator's Guide for information about Oracle ASM disk discovery