2.2.2 Understanding Oracle ASM Disk Groups for Oracle Exadata Storage Servers

This topic explains Oracle Automatic Storage Management (Oracle ASM) disk groups, and how to create an Oracle ASM disk group for Oracle Exadata System Software using the CREATE DISKGROUP SQL command.

Before creating an Oracle ASM disk group, determine which grid disks belong to the Oracle ASM disk group. It is recommended that you choose similar names for the Oracle ASM disk group and its grid disks whenever possible.

The Oracle Exadata Storage Server grid disks are specified with the following pattern:

o/cell_IPaddress/griddisk_name

In the preceding syntax, cell_IPaddress is the IP address of Oracle Exadata Storage Server, and griddisk_name is the name of the grid disk.

The cell discovery strings begin with the o/ prefix.

When specifying the grid disks to be added to the disk group, consider the following:

• The default Oracle ASM disk name is the grid disk name. Oracle recommends using the default name.
• The default failure group name is the cell name. Oracle recommends using the default name.
• Wildcards in the form of '*' may be used in the cell_IPaddress or griddisk_name to add multiple disks with one command. For example:

  CREATE DISKGROUP reco HIGH REDUNDANCYDISK 'o/*/DATA*'

When a failure group is not specified, Oracle ASM adds each disk within its own failure group. However, when the disks are stored on Oracle Exadata Storage Servers and a failure group is not specified, Oracle ASM adds a disk to the failure group for that cell. The failure group name is the cell name.

Note:

If a cell is renamed, and a disk from that cell is added to an existing disk group that has disks from that cell, then Oracle ASM adds the new disk to a failure group using the new cell name. To ensure all the disks from the cell are in one failure group, add the disk to the disk group and specify the original failure group name.

To enable Smart Scan predicate offload processing, all disks in a disk group must be Oracle Exadata Storage Server grid disks. You cannot include conventional disks with Oracle Exadata Storage Server grid disks.

• About Fast Disk Scan Rates
  
• Setting the Oracle ASM Content Type
  Setting the content.type disk group attribute enhances fault tolerance, especially for normal redundancy disk groups.