Back in April I was at COLLABORATE 08 and delivered a presentation on 11g — Oracle 11g New Features Out of the Box, including Oracle 11g ASM features. The first ASM slide was about diskgroup compatibility, and I have a bit more to share than I said back then.

Every diskgroup in ASM has two compatibility attributes — compatible.asm and compatible.rdbms. In 10.2, the V$ASM_DISKGROUP view has a couple new columns added — COMPATIBILITY and DATABASE_COMPATIBILITY, but only in 11g did Oracle introduce the concept of diskgroup attributes and the V$ASM_ATTRIBUTE view. Thus, there are two ways to check the diskgroup attributes in 11g:

SQL> col COMPATIBILITY form a10
SQL> col DATABASE_COMPATIBILITY form a10
SQL> col NAME form a20
SQL> select group_number, name,
compatibility, database_compatibility from v$asm_diskgroup;

GROUP_NUMBER NAME                 COMPATIBIL DATABASE_C
------------ -------------------- ---------- ----------
           1 DG1                  11.1.0.0.0 11.1.0.0.0
           2 DG2                  10.1.0.0.0 10.1.0.0.0

SQL> col value form a10
SQL> select group_number, name, value from v$asm_attribute;

GROUP_NUMBER NAME                 VALUE
------------ -------------------- ----------
           1 disk_repair_time     3.6h
           1 au_size              1048576
           1 compatible.asm       11.1.0.0.0
           1 compatible.rdbms     11.1

Note that V$ASM_ATTRIBUTES is filled only when compatible.asm is set to 11.1. What’s important is that you can only change compatibility level upwards; there is no way to reset it back to the lower value. Compatibility attributes can be changed online one at a time:

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