Oracle Database 10g introduced Automatic Storage Management (ASM) which provides a file system and volume manager in the database, enabling automated striping of files and automating mirroring of database extents. DBAs simply define 1) a pool of storage or 2) disk group and manage the disk group through Enterprise Manager. Disk groups are created with normal redundancy as the default (2-way mirroring). You can also create disk groups with high redundancy (3-way mirroring) or external redundancy (no mirroring).
Failure groups are ASM disks that share a common failure point, so mirroring will automatically occur to a different failure group to provide high availability. Oracle manages the files that are stored in ASM disk groups. ASM can manage Oracle datafiles, logfiles, control files, archive logs, and RMAN/backup sets. Workloads can be dynamically rebalanced as storage is reconfigured such that when storage is added or removed from the pool, data can be redistributed in the background.