What are the key components of Oracle Automatic Storage Management (ASM)?

Oracle Automatic Storage Management (ASM) is a feature of Oracle Database that simplifies the management of database files by providing a logical volume manager and file system specifically designed for Oracle database files. Here's a technical breakdown of its key components:

  1. Disk Groups: Disk groups are the fundamental storage entities in ASM. A disk group is a collection of disks that are managed as a single unit by ASM. These disks can be physical disks, partitions, or logical volumes. Disk groups provide the underlying storage infrastructure for Oracle database files such as data files, control files, redo log files, and archived log files.
  2. ASM Instance: ASM operates as an instance within the Oracle Database architecture. It has its own memory structures and background processes similar to a regular Oracle Database instance. The ASM instance is responsible for managing disk groups, allocating storage space, and performing I/O operations on behalf of the database instances that use ASM for storage.
  3. ASM Disk: An ASM disk is a physical storage device that is managed by ASM. Before ASM can use a disk, it must be initialized and marked as an ASM disk. ASM disks can be either whole disks or partitions. Once added to a disk group, ASM manages the allocation of space on these disks and ensures that data is evenly distributed across the available disks for performance and redundancy purposes.
  4. ASM Disk Group Attributes: Disk groups in ASM have configurable attributes that define their behavior and characteristics. These attributes include properties such as redundancy level (e.g., high redundancy, normal redundancy, or external redundancy), striping attributes (e.g., fine or coarse), and allocation unit size (AU size). These attributes can be set at the time of disk group creation or modified later as needed.
  5. Mirroring and Striping: ASM provides built-in support for both mirroring and striping of data to ensure high availability and performance. Mirroring, also known as redundancy, involves maintaining multiple copies (mirrors) of data across different disks to protect against disk failures. Striping involves distributing data across multiple disks to improve I/O performance by parallelizing disk access operations.
  6. ASM Files: ASM manages database files as ASM files within disk groups. These files include data files, control files, redo log files, and archived log files. ASM abstracts the physical storage details from the database instances and presents the ASM files as regular files to the database.
  7. ASM Instance Management Tools: ASM provides a set of command-line utilities and APIs for managing ASM instances, disk groups, and ASM disks. These tools include asmcmd for managing ASM from the command line, SQL*Plus commands for managing ASM instances, and various APIs for programmatic interaction with ASM.
  8. ASM Cluster File System (ACFS): In addition to managing Oracle database files, ASM can also be used to manage general-purpose files through a feature called ASM Cluster File System (ACFS). ACFS extends the capabilities of ASM to provide a POSIX-compliant file system that can be used to store non-database files such as application binaries, configuration files, and user data files.