Data files, redo logs, and RMAN backup pieces must be stored in different ASM disk groups for optimal performance.

All ASM Disks belonging to a disk group should be of the same size for optimal performance.

Hardware-based mirroring combined with ASM mirroring guarantees optimal performance.

All ASM Disks belonging to a disk group should have the same hardware specifications and storage attributes for optimal performance.

To improve performance a database must have two disk groups; one for data and one for the fast recovery area.