Oracle Database - ASM - Disk group


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.

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.

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.

How to

get the disk groups

SELECT name, type, total_mb, free_mb, required_mirror_free_mb, 
usable_file_mb FROM V$ASM_DISKGROUP;

Documentation / Reference

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