Enable new ASM features in Oracle Grid Infrastructure 11gR2
Oracle GRID Infrastructure 11gR2 introduces many great ASM features. However most of them are disabled by default even if you run Oracle 11gR2 database on it. Below I share some clarify on how to enable new ASM 11g features for your 11g database.
In Oracle 11g, an ASM instance can support different RDBMS clients running at different compatibility settings. A database instance can use both Oracle database 10g and 11g disk groups. Furthermore Oracle introduced additional three kinds of compatibility attributes applicable to ASM disk groups. These attributes are called ASM compatibility, RDBMS compatibility, and ADVM compatibility, respectively. When creating or altering a disk group, you can specify the COMPATIBLE.ASM, COMPATIBLE.RDBMS and COMPATIBLE.ADVM disk group attributes.
All these compatibility settings depend to each other and in fact define the ASM functionality and enable new 11g ASM features. Let’s review them all
ASM disk group compatibility attribute
It determines the minimum software version for an Oracle ASM instance that can use the disk group. This setting affects the format of the data structures for the Oracle ASM metadata on the disk and also enables most of the 11g features. The ASM compatibility level of a disk group must be advanced before advancing other disk group compatibility attributes and its value must be greater than or equal to the value of other disk group compatibility attributes.
RDBMS disk group compatibility attribute
It refers to the minimum compatible version of the RDBMS instance that would allow the instance to mount the disk group. It also however enables new 11g ASM features for the corresponding disk group.
ADVM disk group compatibility attribute
It determines whether the disk group can contain Oracle ASM volumes. The value must be set to 11.2 or higher. By default, the value of the COMPATIBLE.ADVM attribute is empty until set.
COMPATIBLE parameter of RDBMS instance
It enables you to use a new release of Oracle Database, while at the same time guaranteeing backward compatibility with an earlier release. It must be greater than or equal to the RDBMS compatibility attribute of ASM disk groups it accesses.
COMPATIBLE parameter of ASM instance
It represents by the default the ASM / Grid Infrastructure binaries version
As summary, even if you COMPATIBILITY = 18.104.22.168 in both ASM and RDBMS instances, the new ASM 11g features are not enabled. The problem is that, if not explicitly specified, both the ASM and RDBMS compatibility disk group attributes default to 10.1. So to be able to use new ASM features, such as Fast Mirror Resync, Preferred read failure groups, variable size extents, etc., both the COMPATIBLE.ASM and COMPATIBLE.RDBMS disk group attributes must be set to a value of 11.1 or higher.
Note that after you advance these attributes, you cannot modify them back to a lower value.
See below the compatibility parameters dependancies
See the list of ASM features from the Oracle documentation: