Oracle Automatic Storage Management (ASM) is a volume manager and a file system for Oracle Database files that supports Single-Instance Oracle Database and Oracle RAC configurations.
Oracle ASM is Oracle's recommended storage management solution that provides an alternative to conventional volume managers, file systems, and raw devices.
Oracle ASM uses disk groups to store data files. An Oracle ASM disk group is a collection of disks that Oracle ASM manages as a unit. You can add or remove disks from a disk group while a database continues to access files from the disk group.
Oracle ASM disk can be configured with either Oracle ASMLib or Oracle ASMFD or Linux udev rules for device persistence.
More information about Oracle Database Architecture can be found here.