2.2.2.2 Setting the Oracle ASM Content Type

Setting the content.type disk group attribute enhances fault tolerance, especially for normal redundancy disk groups.

Commencing with Oracle Grid Infrastructure release 11.2.0.3, Oracle ASM provides administrators with the option to specify the content type associated with each disk group. This capability is provided by the content.type disk group attribute. Three possible settings are allowed: data, recovery, or system. Each content type setting modifies the adjacency measure used by the secondary extent placement algorithm.

The result is that the contents of disk groups with different content type settings are distributed differently across the available disks. This decreases the likelihood that a double failure will result in data loss across multiple normal redundancy disk groups with different content type settings. Likewise, a triple failure is less likely to result in data loss on multiple high redundancy disk groups with different content type settings.

The value of content.type attribute should be set as follows:

• DATA and SPARSE disk groups — data

• RECO disk group — recovery

• DBFS_DG disk group (if present) — system

Following this recommendation enhances fault-tolerance. For example, even if the DATA and RECO disk groups use normal redundancy, at least one of the disk groups will remain if two disks fail simultaneously. Therefore, even if DATA is dismounted, databases can typically be recovered from backup objects in RECO.

Note:

• Do not use the content.type attribute to distinguish the availability characteristics of disk groups that are used for a different purpose, such as those created to support a particular service.

• The Oracle Database and Oracle Grid Infrastructure software must be release 12.1.0.2.0 BP5 or later when using sparse grid disks.

1. Use the ALTER DISKGROUP command to set the content.type attribute for an existing disk group, and then rebalance the disk group.

   For example:

   ALTER DISKGROUP reco SET ATTRIBUTE 'content.type'='recovery';
   ALTER DISKGROUP reco REBALANCE POWER preferred_power_setting ; 
   

   The rebalance operation can take a long time, but the data in the disk group is fully redundant throughout the operation. Oracle ASM monitors the rebalance operation, and Oracle Exadata System Software sends an e-mail message when the operation completes.

2. Check the content.type attributes using the following query:

   SQL> SELECT dg.name,a.value FROM v$asm_diskgroup dg,        \
        v$asm_attribute a WHERE dg.group_number=a.group_number \
        AND a.name='content.type' AND (dg.name LIKE 'DATA%'    \
        OR dg.name LIKE 'RECO%' OR dg.name LIKE 'DBFS_DG%');
    
   NAME                 VALUE
   -------------------- --------------------
   DATA                 data
   RECO                 recovery
   DBFS_DG              system

Example 2-1 Specifying content.type While Creating a Disk Group

In this example, the compatible.rdbms attribute is set to 11.2.0.2 in order to support both Oracle Database release 11.2.0.2 and release 11.2.0.3 databases in a consolidated environment.

CREATE DISKGROUP data NORMAL REDUNDANCY
DISK 'o/*/DATA*'
ATTRIBUTE 'content.type' = 'DATA',
'AU_SIZE' = '4M',
'cell.smart_scan_capable'='TRUE',
'compatible.rdbms'='11.2.0.2',
'compatible.asm'='11.2.0.3';