Provide the name of the initial disk group you configure in the Disk Group Name field.
The Add Disks table displays disks that are configured as candidate disks. Select the number of candidate disks (or partitions on a file system) required for the level of redundancy you want for your first disk group.
For standard disk groups, High redundancy requires a minimum of three disks. Normal requires a minimum of two disks. External requires a minimum of one disk.
If you want to install Oracle Cluster Registry and voting disk files on Oracle ASM, then the minimum number of disks is higher. High redundancy requires a minimum of five disks. Normal redundancy requires a minimum of three disks. External redundancy requires a minimum of one disk.
Voting disk files require a higher number of minimum disks, to provide the required separate physical devices for quorum failure groups, so that a quorum of voting disk files are available even if one failure group becomes unavailable. If you want to place voting disk files on Oracle ASM, then ensure that you have enough disks available for the redundancy level you require.
If you do not see candidate disks displayed, then click Change Discovery Path, and enter a path where Oracle Universal Installer (OUI) can find candidate disks.
For additional information, review the following sections:
An ASM disk group consists of multiple disks. The disk group is the fundamental object that ASM manages. Each disk group contains the metadata that is required for the management of space in the disk group. Files are allocated from disk groups. Any ASM file is completely contained within a single disk group. However, a disk group might contain files belonging to several databases and a single database can use files from multiple disk groups. For most installations you need only a small number of disk groups, usually two, and rarely more than three. Disk group components include disks, files, and allocation units.
A Candidate Disk is a disk that is not part of an existing disk group. If you want to use a disk that previously had been a member of an ASM disk group, and was not deleted properly from the disk group (as in an incomplete installation), then delete existing information on the disk so that it can be recognized as a candidate disk.
Redundancy, or mirroring, is the process of replicating the contents of a file in another location. Redundancy protects data integrity by storing copies of data on multiple disks. The disk group type determines the mirroring levels with which Oracle creates files in a disk group.
When you create a disk group, you specify an ASM disk group type based on one of the following three redundancy levels:
High: Three-way mirroring
Normal: Two-way mirroring
External: Choosing not to use ASM mirroring of files, commonly when you provide mirroring using another technology, such as a Redundant Array of Independent (or Inexpensive) Disks (RAID).
The disk group type determines the mirroring levels with which Oracle creates files in a disk group. The redundancy level controls how many disk failures are tolerated without dismounting the disk group or losing data.
Every Oracle ASM disk is divided into allocation units (AU). An allocation unit is the fundamental unit of allocation within a disk group. A file extent consists of one or more allocation units. An Oracle ASM file consists of one or more file extents.
When you create a disk group, you can set the Oracle ASM allocation unit size with the AU_SIZE disk group attribute. The values can be 1, 2, 4, 8, or 16 MB, depending on the specific disk group compatibility level. Larger AU sizes typically provide performance advantages for data warehouse applications that use large sequential reads.
The default value is set to 1MB.