Oracle ASM and Oracle ACFS both use Oracle ASM disk storage. Oracle ASM presents disk groups to the database as mounted storage. Oracle ACSF presents Oracle ADVM volumes to the operating system as mount points.
Oracle ASM disk storage has two organizations: physical and logical. The physical is Oracle ASM disks. Oracle ASM disks are physical disk partitions that are assigned to Oracle ASM. These may be full disks or disk partitions. Each disk group has two or more failure groups, except when redundancy is set to EXTERNAL.
The unit of organization of Oracle ASM disk storage is a disk group. Each disk group has two or more Oracle ASM disks assigned to a disk group. Each Oracle ASM disk can only be assigned to one disk group. Disk groups have properties that determine their behavior, such as redundancy and failure groups.
You may set the redundancy property of the disk group to EXTERNAL (no-mirroring), NORMAL (two-way mirroring), HIGH (three-way mirroring), EXTENDED, or FLEX. See Creating a Disk Group for more information about Redundancy properties. When Redundancy is set to FLEX, the mirroring is set for the file group rather than the disk group.