Overview of Automatic Storage Management (ASM)

Automatic Storage Management (ASM) is an option and a new feature of Oracle 10g and onwards that simplifies the storage management for all Oracle database file types. It renders the capabilities of a volume manager and filesystem together into
the Oracle database kernel. Although, it inherits the Stripe And Mirror Everything (SAME) functionality, it strips the data (extents) evenly across the ASM disks of a disk group by default and provides the mirroring functionality as an option. The
management and administration of ASM is made easy through a well-known set of SQL statements, such as, CREATE, ALTER, DROP, and through GUI tools.

While the ASM was initially intended for managing and maintaining only the Oracle database files and other related files, its functionality has been significantly improved in 11g R1 and R2 versions to manage all types of data. The following are some of the key features and benefits of ASM:

• It simplifies the storage configuration management for Oracle datafiles and other files.
• It eliminates the need for third-party software, (for example, volume manager) to manage the storage for the databases.
• When a datafile is created, it is divided into equally sized (1, 2, 4, 8, 16, 32,or 64 MB) extents that are scattered evenly across the disks of a disk group to provide balanced I/O to improve performance and prevent hot spot symptoms.
• It is built on the Stripe and Mirror Everything (SAME) functionality.
• It supports both non-RAC and RAC databases efficiently.
• It has the ability to add and remove ASM disks online without actually disturbing the ongoing operations.
• It can be managed and administrated using a set of known SQL statements.
• It performs automatic online redistribution for the data whenever a disk is being added or dropped.
• With ASM 11g R2, in addition to all database file types, it can also be used to store non-Oracle datafile types such as binaries, images, and so on. Beginning with ASM 11g R2, it provides the ability of a preferred read functionality, when ASM mirroring features are enabled.
• It supports multiversioning of databases.
• It supports a multipathing feature to prevent outages from disk path failures.