Oracle ASM is a storage management solution for Oracle databases and clusters providing volume management and a filesystem,
Oracle Automatic Storage Management is Oracle's recommended volume management solution. It provides an alternative to raw device, filesystems, and operating-system volume managers.
Data is striped across disks, and optionally mirrored two- or three-way. ASM can handle different fault tolerance requirements via its flexible failure groups, which can span one or more disks (for example, all disks attached to a single storage controller may be in one failure group, to allow for failure of the controller).
Database files can be stored using either Oracle Managed Files or manual file names. Non-database files can be stored using the ASM Cluster File System.
Documentation is available principally in the Automatic Storage Management Administrator’s Guide.