Oracle Database - ASM (Automatic Storage Management)
About
Starting with Oracle Database 10g (10.1.0.3 or later), Automatic Storage Management is a high-performance storage management solution. For Oracle Database files, it simplifies the management of a dynamic database environment, such as creating and laying out databases and managing disk space.
Automatic Storage Management can support multiple databases then it manages the storage of all database files, such as:
- and data pump export files.
Automatic Storage Management can manage the Oracle Database executable binary files as well as any other non-database file by creating a file system with Oracle Automatic Storage Management Cluster File System. Though Oracle Automatic Storage Management Cluster File System is cluster aware it works as a file system on a single instance database also.
At a high level, implementing Automatic Storage Management involves allocating partitioned disks for Oracle Database with preferences for striping and mirroring.
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Striping and Mirroring
ASM will stripe across all devices you present to it in the context of a disk group. Most importantly, if and when you expand your configuration, ASM will automatically re-balance (re-stripe) the data across all devices, so that you will always benefit from all storage devices in your configuration, without running into hot spots in the storage configuration. ASM implements Oracle's S.A.M.E. methodology (Stripe And Mirror Everything using a stripe size of 1 MB) and automatically maintains it as devices are added or removed. ASM can also be used to mirror data or it can be used with hardware RAID configurations.
Benefits
Automatic Storage Management manages the disk space for you. This helps avoid the need for traditional disk management tools, such as:
and the numerous commands necessary to manage both.
The synchronization between Automatic Storage Management and the database instance is handled by CSS.
Installation
Automatic Storage Management can be used with single database installations, multiple database installations, and in Oracle RAC environments. It can be used with databases created in Oracle Database 10g Release 1 (10.1.0.3 or later).
However, Oracle Database 11g Release 2 (11.2) databases must use Automatic Storage Management from Oracle Database 11g Release 2 (11.2) or later. Automatic Storage Management is installed as part of the grid infrastructure installation. If you plan to use Automatic Storage Management, then you must install the grid infrastructure before installing your database.
Oracle recommends that you have the Automatic Storage Management instance in its own Oracle home. Oracle also recommends that you run this instance before you start a database instance that uses Automatic Storage Management.
For an Oracle Database installation, you only need one Automatic Storage Management instance, regardless of the number of database instances on the computer.
Component
The following are components of an Automatic Storage Management installation:
- Automatic Storage Management Disk Groups
A disk group is a set of disk devices that Automatic Storage Management manages as a single unit. Each disk device can be an individual physical disk, a multiple disk device, such as a RAID storage array or logical volume, or even a partition on a physical disk. However, in most cases, disk groups consist of one or more individual physical disks. To enable Automatic Storage Management to balance input-output operation and storage efficiently within the disk group, you must ensure that all devices in the disk group have similar, if not identical, storage capacity and performance.
- Automatic Storage Management Instance
The Automatic Storage Management instance is a special Oracle instance that manages Automatic Storage Management disk groups. The Automatic Storage Management instance and the ASMSNMP account are created and started, if necessary, when you install Oracle grid infrastructure. Oracle Enterprise Manager uses this account to monitor ASM instances to retrieve data from ASM-related data dictionary views. The ASMSNMP account status is set to OPEN upon creation, and it is granted the SYSDBA privilege.
Storage Resources for Asm Disk Groups
You can create an Oracle ASM disk group using one of the following storage resources:
- Disk Partition
A disk partition can be the entire disk drive or a section of a disk drive. However, the Oracle ASM disk cannot be in a partition that includes the partition table because the partition table would be overwritten.
A LUN is a disk presented to a computer system by a storage array. Oracle recommends that you use hardware RAID functionality to create LUNs. Storage hardware RAID 0+1 or RAID5, and other RAID configurations, can be provided to Oracle ASM as Oracle ASM disks.
A logical volume is supported in less complicated configurations where a logical volume is mapped to a LUN, or a logical volume uses disks or raw partitions. Logical volume configurations are not recommended by Oracle because they create a duplication of functionality. Oracle also does not recommended using logical volume managers for mirroring because Oracle ASM provides mirroring.
An Oracle ASM disk group can be created from NFS files, including Oracle Direct NFS (dNFS), as well as whole disks, partitions, and LUNs. The NFS files that are provisioned to a disk group may be from multiple NFS servers to provide better load balancing and flexible capacity planning.
Direct NFS can be used to store data files, but is not supported for Oracle Clusterware files. To install Oracle Real Application Clusters (Oracle RAC) on Windows using Direct NFS, you must also have access to a shared storage method other than NFS for the Oracle Clusterware files.
