Creating Disk Groups

Creating Disk Groups

·         Using the CREATE DISKGROUP SQL Statement

·         Creating Disk Groups for a New Oracle Installation

Using the CREATE DISKGROUP SQL Statement

The CREATE DISKGROUP SQL statement is used to create disk groups. When creating a disk group, you:

·         Assign a unique name to the disk group.

·         Specify the redundancy level of the disk group.

·         Specify the disks that are to be formatted as Oracle ASM disks belonging to the disk group.

·         Optionally specify the disks as belonging to specific failure groups.

·         Optionally specify the type of failure group.

·         Optionally specify disk group attributes, such as software compatibility or allocation unit size.

Example: Creating a Disk Group

The following examples assume that the ASM_DISKSTRING initialization parameter is set to the '/devices/*' string. Oracle ASM disk discovery identifies disks in the /devices directory, including the following disks:
Controller 1:

/devices/diska1
/devices/diska2
/devices/diska3
/devices/diska4

Controller 2:
/devices/diskb1
/devices/diskb2
/devices/diskb3
/devices/diskb4

The SQL statement Example creates a disk group named data with normal redundancy consisting of two failure groups controller1 or controller2 with four disks in each failure group. The data disk group is typically used to store database data files.

Example Creating the DATA disk group

CREATE DISKGROUP data NORMAL REDUNDANCY

  FAILGROUP controller1 DISK

    '/devices/diska1' NAME diska1,

    '/devices/diska2' NAME diska2,

    '/devices/diska3' NAME diska3,

    '/devices/diska4' NAME diska4

  FAILGROUP controller2 DISK

    '/devices/diskb1' NAME diskb1,

    '/devices/diskb2' NAME diskb2,

    '/devices/diskb3' NAME diskb3,

    '/devices/diskb4' NAME diskb4

  ATTRIBUTE 'au_size'='4M',

    'compatible.asm' = '11.2',

    'compatible.rdbms' = '11.2',

    'compatible.advm' = '11.2';

In above Example the NAME clauses enable you to explicitly assign names to the disks rather than the default system-generated names. The system-generated names are in the form diskgroup_nnnn, where nnnn is the disk number for the disk in the disk group. For ASMLib disks, the disk name defaults to the ASMLib name that is the user label of the disk; for example, mydisk is the default Oracle ASM disk name for ORCL:mydisk.

When creating the disk group in above example, the values of following disk group attributes were explicitly set:

• AU_SIZE

Specifies the size of the allocation unit for the disk group. You can view the value of the AU_SIZE disk group attribute in the ALLOCATION_UNIT_SIZE column of the V$ASM_DISKGROUP view.

• COMPATIBLE.ASM

Determines the minimum software version for any Oracle ASM instance that uses a disk group. COMPATIBLE.RDBMS

Determines the minimum software version for any database instance that uses a disk group. COMPATIBLE.ADVM

Determines whether the disk group can contain Oracle ASM volumes.