Automatic Storage Management
Automatic Storage Management (ASM), an Oracle Database feature, simplifies storage management and ensures consistency across all server and storage platforms. ASM manages storage through a small number of storage pools known as ASM Disk Groups. Database-related files are assigned to ASM Disk Groups, and ASM maintains the structure and data organization to ensure maximum performance and protection against storage hardware failure.
ASM Disk Groups are a quick and easy way to consolidate storage and simplify administrative responsibilities previously performed by DBAs and System Administrators. ASM provides the fundamental storage management for the ASM Cluster File System (ACFS), which offers centralized storage for data stored outside of the database.
Oracle ASM Provides the following Benefits :
1. Striping
Oracle ASM distributes data uniformly across all drives in a disk group to maximize performance and utilization. The even distribution of database files eliminates the need for ongoing monitoring and I/O performance adjustment.
For example:
If a disk group contains six disks, bits of each Oracle ASM file are written to each of them. These parts are referred to as extents. In this case, the components are in 1 MB chunks. When a database file is generated, it is striped (split into extents and spread) across the six disks, and the allocated disk space on all six disks increases uniformly. When reading the file, file extents are read in parallel from all six disks, which significantly improves performance.
2. Mirroring
Oracle ASM can improve availability by replicating any file. Oracle ASM replicates files, as opposed to operating system mirroring, which reflects the disk. Mirroring refers to remaining redundant copies, or mirrored copies, of each extent of a file in order to prevent data loss due to disk failures. The mirrored copy of each file extent is always stored on a separate disk from the original copy. If a disk fails, Oracle ASM can still access affected files by accessing mirrored copies on the remaining disks in the disk group.
Oracle ASM supports two types of mirroring: 2-way mirroring, which provides one mirrored copy for each file extent, and 3-way mirroring, which provides two mirrored copies per file extent.
3. Online storage reconfiguration and dynamic rebalancing
Oracle ASM allows you to add and remove disks from your storage system while the database is running. When you add a disk, Oracle ASM automatically redistributes the data so that it is evenly distributed over all disks in the disk group, including the new one. This dispersal is known as rebalancing. It is done in the background and has little impact on database speed. When you request to delete a disk, Oracle ASM rebalances the disk group by equally moving all file extents from the removed disk to the remaining disks.
4. Managed file creation and deletion
Oracle ASM significantly simplifies administrative duties by making files stored in Oracle ASM disk groups Oracle Managed Files. When files are created, Oracle ASM assigns them names and deletes them when they are no longer needed.
Oracle recommends using Oracle ASM for database file storage rather than raw devices or the operating system's file system. However, databases can contain both Oracle and non-Oracle ASM files. Oracle Enterprise Manager contains a wizard for upgrading non-Oracle ASM database files to Oracle ASM.
The Oracle ASM instance
Oracle ASM is built as a unique Oracle instance, complete with System Global Area and background activities. Oracle ASM is strongly connected with the database instance. Every server that runs one or more database instances and stores them with Oracle ASM has an Oracle ASM instance. In an Oracle Real Application Clusters environment, each node has its own Oracle ASM instance, which communicates with each other on a peer-to-peer basis. Regardless of how many database instances are present on a node, only one Oracle ASM instance is required.
Key Benefits of ASM
- Simplifies and automates storage management
- Improves storage efficiency and agility.
- Delivers consistent performance, availability, and scalability.
- Support database failure in case of server failure.
- ACFS integrates storage management.
