Overview

Automatic Storage Management (ASM) is a feature in Oracle Database 10g/11g that provides the database administrator with a simple storage management interface that is consistent across all server and storage platforms. As a vertically integrated file system and volume manager, purpose-built for Oracle database files, ASM provides the performance of async I/O with the easy management of a file system. ASM provides capability that saves the DBAs time and provides flexibility to manage a dynamic database environment with increased efficiency.

Advantages of ASM?

Disk Addition—Adding a disk becomes very easy. No downtime is required and file extents are redistributed automatically.
I/O Distribution—I/O is spread over all the available disks automatically, without manual intervention, reducing chances of a hot spot.
Stripe Width—Striping can be fine grained as in Redo Log Files (128K for faster transfer rate) and coarse for datafiles (1MB for transfer of a large number of blocks at one time).
Buffering—The ASM filesystem is not buffered, making it direct I/O capable by design.
Kernelized Asynch I/O—There is no special setup necessary to enable kernelized asynchronous I/O, without using raw or third-party filesystems such as Veritas Quick I/O.
Mirroring—Software mirroring can be set up easily, if hardware mirroring is not available.