Automatic Storage Management (ASM) is an Oracle database feature that provides DBAs with a simple storage management interface that is consistent across all server and storage platforms.
ASM is an integrated volume manager for storing Oracle database files – including datafiles, redo logs, backups, controlfiles and spfiles. ASM allows administrators to add and remove disks while the database is on-line and available to users. Data is automatically striped across all disks in a disk group, and is optionally mirrored.