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.
File System Components
Shows the maximum number of log switches per day
Shows the average number of log switches per day
The redo log size
The maximum number of megabytes required per day
Since some DBAs want to size the archived redo log file system to hold two days' worth of updates,
this column shows the maximum amount of redo log space over a two-day period.