--- title: Oracle 11g ASM Diskgroup Compatibility description: 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. --- [Blog | Pythian ](https://www.pythian.com/blog) # [Oracle 11g ASM Diskgroup Compatibility](https://www.pythian.com/blog/oracle-11g-asm-diskgroup-compatibility) Written by [Pythian Marketing](https://www.pythian.com/blog/author/pythian-marketing) | Jun 18, 2008 4:00:00 AM Back in April I was at COLLABORATE 08 and delivered a presentation on 11g — [Oracle 11g New Features Out of the Box](https://blog.pythian.coms/951/alex-gorbachev-at-collaborate-08/), 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`. ## Checking diskgroup attributes in 11g 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: ``` ------------ -------------------- ---------- ---------- ``` Note that `V$ASM_ATTRIBUTES` is filled only when `compatible.asm` is set to 11.1. What’s important is that you can only change compatibility level upwards; there is no way to reset it back to the lower value. ## Changing compatibility levels online Compatibility attributes can be changed online one at a time: ``` SQL> alter diskgroup dg2 set attribute 'compatible.asm'='11.1'; Diskgroup altered. SQL> alter diskgroup dg2 set attribute 'compatible.rdbms'='11.1'; Diskgroup altered. SQL> select group_number, name, compatibility, database_compatibility from v$asm_diskgroup; GROUP_NUMBER NAME COMPATIBIL DATABASE_C ------------ -------------------- ---------- ---------- 1 DG1 11.1.0.0.0 11.1.0.0.0 2 DG2 11.1.0.0.0 11.1.0.0.0 ``` What are compatibility attributes are useful for? They are very handy for upgrades and migrations when ASM diskgroups need to be available for ASM instances and database instances of different versions. Depending on the migration path, you might need to be able to access some diskgroups from different versions of ASM and different database instances. It might also be useful for transportable tablespaces between 10g and 11g databases. The `compatible.asm` diskgroup attribute controls the format of the ASM diskgroup metadata. Only ASM instances with a software version equal to or greater than `compatible.asm` can mount the diskgroup. The `compatible.rdbms` diskgroup attribute determines the format of ASM files themselves. The diskgroup can be accessed by any database instance with a compatible `init.ora` parameter set equal to or higher than the `compatible.rdbms` attribute. Note that the `compatible.rdbms` attribute can be set to 10.2 as well, but I couldn’t see if there were any differences in the feature set except that the `compatible.rdbms=10.2` setting requires a database instance with the compatible parameter set to 10.2 or higher. `compatible.asm` cannot be set below 11.1 except when it’s already 10.1 by default. The `compatible.rdbms` attribute can be changed only if `compatible.asm` is advanced to 11.1. Otherwise, you get the following error message: ``` SQL> alter diskgroup dg2 set attribute 'compatible.rdbms'='11.1'; alter diskgroup dg2 set attribute 'compatible.rdbms'='11.1' * ERROR at line 1: ORA-15032: not all alterations performed ORA-15242: could not set attribute compatible.rdbms ORA-15221: ASM operation requires compatible.asm of 11.1.0.0.0 or higher ``` ## Controlling default compatibility with hidden parameters When creating a new diskgroup, compatibility attributes can be explicitly specified. It is interesting that the default is still 10.1 for both attributes even when the diskgroup is created from an ASM 10g instance and all connected databases are of 11g version. Oracle is conservative here. During the COLLABORATE presentation, Jeremy Schneider asked me if there is a way to control the default compatibility version and, at that time, I didn’t know how to set the default compatibility to 11.1. Now that I have had a bit of time to look into it, I found couple hidden underscore parameters: `_asm_compatibility` and `_rdbms_compatibility`: ``` SQL> select i.ksppinm, v.ksppstvl from x$ksppi i, x$ksppcv v 2 where i.ksppinm in ('_rdbms_compatibility','_asm_compatibility') 3 and i.indx=v.indx; KSPPINM KSPPSTVL ------------------------------ ---------- _asm_compatibility 10.1 _rdbms_compatibility 10.1 ``` Let’s test. ``` ------------------------------ ---------- ``` Now what features are available with different compatibility settings? ### **Diskgroup attributes** `compatible.asm` — 11.1 `compatible.rdbms` — any ### **Non-default allocation unit size** For AU sizes 1-8 MB, both compatibility attributes can be 10.1. ``` ------------ -------------------- ---------- ---------- ``` The absence of the attribute `au_size` in `V$ASM_ATTRIBUTE` is confusing, but recall that attributes are displayed only when `compatible.asm` is set to 11.1. ``` ------------ -------------------- -------------------- ``` For AU sizes 16-64 MB both compatibility attributes must be 11.1. ### **The rest of 11g’s ASM new features** Fast mirror resync, variable size extents, preferred read failure groups Both `compatible.asm` and `compatible.rdbms` must be set to 11.1. It looks like one of our customers is going to production with the new 11g RAC cluster on ASM using some of these new ASM features, so I’m looking forward to see how well it works in real life. ## Oracle Database Consulting Services Ready to optimize your Oracle Database for the future?   [View full post](https://www.pythian.com/blog/oracle-11g-asm-diskgroup-compatibility) ```json { "@context" : "http://schema.org", "@type" : "BlogPosting", "author" : { "@type" : "Person", "name" : "Pythian Marketing" }, "dateModified" : "2026-02-01T20:05:49.696Z", "datePublished" : "2008-06-18T04:00:00Z", "headline" : "Oracle 11g ASM Diskgroup Compatibility", "image" : { "@type" : "ImageObject", "height" : 60, "url" : "/hs/hsstatic/content_shared_assets/static-1.4092/img/default-amp-logo.png", "width" : 60 }, "mainEntityOfPage" : "https://www.pythian.com/blog/oracle-11g-asm-diskgroup-compatibility", "publisher" : { "@type" : "Organization", "logo" : { "@type" : "ImageObject", "height" : 60, "url" : "/hs/hsstatic/content_shared_assets/static-1.4092/img/default-amp-logo.png", "width" : 60 }, "name" : "Pythian Blog" } } ```