Using the CREATE DISKGROUP SQL Statement

You can use CREATE DISKGROUP SQL statement to create disk groups. When creating a disk group, you:

Assign a unique name to the disk group.

The specified disk group name is not case sensitive and is always converted to uppercase when stored internally.

Note:

Oracle does not recommend using identifiers for database object names that must be quoted. While these quoted identifiers may be valid as names in the SQL CREATE statement, such as CREATE DISKGROUP "1DATA", the names may not be valid when using other tools that manage the database object. For more information about naming database objects, refer to Oracle Database SQL Language Reference.
Specify the redundancy level of the disk group.

For Oracle ASM to mirror files, specify the redundancy level as NORMAL REDUNDANCY (2-way mirroring by default for most file types) or HIGH REDUNDANCY (3-way mirroring for all files). Specify EXTERNAL REDUNDANCY if you do not want mirroring by Oracle ASM. For example, you might choose EXTERNAL REDUNDANCY to use storage array protection features.

After a disk group is created, you cannot alter the redundancy level of the disk group. To change the redundancy level, you must create another disk group with the appropriate redundancy and then move the files to the new disk group.

Oracle recommends that you create failure groups of equal size to maintain space balance and even distribution of mirror data.

For more information about redundancy levels, refer to "Mirroring_ Redundancy_ and Failure Group Options".
Specify the disks that are to be formatted as Oracle ASM disks belonging to the disk group.

The disks can be specified using operating system dependent wildcard characters in search strings that Oracle ASM then uses to find the disks. You can specify names for the disks with the NAME clause or use the system-generated names.
Optionally specify the disks as belonging to specific failure groups.

For information about failure groups, refer to "Understanding Oracle ASM Concepts" and "Mirroring_ Redundancy_ and Failure Group Options".
Optionally specify the type of failure group.

For information about QUORUM and REGULAR failure groups, refer to "Storing Oracle Cluster Registry and Voting Files in Oracle ASM Disk Groups".
Optionally specify disk group attributes, such as software compatibility or allocation unit size.

Oracle ASM programmatically determines the size of each disk. If for some reason this is not possible, or to restrict the amount of space used on a disk, you can specify a SIZE clause for each disk. Oracle ASM creates operating system–independent names for the disks in a disk group that you can use to reference the disks in other SQL statements. Optionally, you can provide your own name for a disk using the NAME clause. Disk names are available in the V$ASM_DISK view.

Note:

A disk cannot belong to multiple disk groups.

The Oracle ASM instance ensures that any disk in a newly created disk group is addressable and is not currently a member of another disk group. You must use FORCE only when adding a disk that was dropped with FORCE. If a disk is dropped with NOFORCE, then you can add it with NOFORCE. For example, a disk might have failed and was dropped from its disk group. After the disk is repaired, it is no longer part of any disk group, but Oracle ASM still recognizes that the disk had been a member of a disk group. You must use the FORCE flag to include the disk in a new disk group. In addition, the disk must be addressable, and the original disk group must not be mounted. Otherwise, the operation fails.

Note:

Use caution when using the FORCE option to add a previously used disk to a disk group; you might cause another disk group to become unusable.

The CREATE DISKGROUP statement mounts the disk group for the first time, and adds the disk group name to the ASM_DISKGROUPS initialization parameter if a server parameter file is being used. If a text initialization parameter file is being used and you want the disk group to be automatically mounted at instance startup, then you must remember to add the disk group name to the ASM_DISKGROUPS initialization parameter before you shut down and restart the Oracle ASM instance. You can also create disk groups with Oracle ASM Configuration Assistant (ASMCA). Refer to "Managing Disk Groups with ASMCA".