Automatic storage management

Automatic Storage Management (ASM) is a feature provided by Oracle Corporation within the Oracle Database from release Oracle 10g (revision 1) onwards. ASM aims to simplify the management of database datafiles, control files and log files. To do so, it provides tools to manage file systems and volumes directly inside the database, allowing database administrators (DBAs) to control volumes and disks with familiar SQL statements in standard Oracle environments. Thus DBAs do not need extra skills in specific file systems or volume managers (which usually operate at the level of the operating system).

ASM creates extents out of datafiles, log-files, system files, control files and other database structures. The system then spreads these extents across all disks in a "diskgroup". One can think of a diskgroup in ASM as an Logical Volume Manager volume group — with an ASM file corresponding to a logical volume. In addition to the existing Oracle background processes, ASM introduces two new ones - OSMB and RBAL. RBAL opens and creates disks in a diskgroup. OSMB provides the functionality of moving data between disks in a diskgroup.

Automatic Storage Management (ASM) simplifies administration of Oracle-related files by allowing the administrator to reference disk groups (rather than individual disks and files) which ASM manages. ASM extends the Oracle Managed Files (OMF) functionality that also includes striping and mirroring to provide balanced and secure storage. DBAs can use the ASM functionality in combination with existing raw and cooked file-systems, along with OMF and manually managed files.

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