Downgrade Oracle Restart 12c – Grid Infrastructure only?

Can you downgrade your Oracle Restart installation from Oracle 12c back to Oracle 11g?

Actually there’s no real direct downgrade supported for Oracle Restart. But of course there’s a way to do it.

Basically it is:

• Deconfigure Oracle Restart in 12c
• Configure Oracle Restart in 11g

But wait a minute. It is very important to know if you have upgraded your database already. If that is the case then first you MUST downgrade your database(s) as you can’t manage a higher version Oracle Database with a lower version Clusterware.

So first of all, please downgrade your Oracle database(s) first:

• Downgrade your database – if you haven’t changed COMPATIBLE during the upgrade!

At the next stage you’ll need to “downgrade” the Oracle Clusterware resp Grid Infrastructure for Oracle Restart:

Before you attempt this you’ll need to deconfigure the Restart resources – and please be aware that here’s a small difference in commands between Oracle 12.1.0.2 and Oracle 12.1.0.1.

This is from the documentation for Oracle 12.1.0.2:

• Deconfigure Oracle Restart 12.1.0.2:
  • Log in as root

  • # cd /u01/app/12.1.0.2/grid/crs/install
    # roothas.sh -deconfig -force

• Once this is complete you can now deinstall the Grid Infrastructure with the deinstall tool
  • See the documentation
• Then you will need either to reinstall the previous – for instance Oracle 11.2.0.4 – Grid Infrastructure or – if it’s still present on the machine – reconfigure it by running root.sh from the previous Clusterware’s home
• And finally reconfigure the database(s) again with Clusterware

  • $ srvctl downgrade database -d db-unique-name -o oraclehome -t to_version

.
In case you’d plan to do this exercise back from Oracle 12.1.0.1 instead then you’ll have different steps to follow to deconfigure Oracle Restart 12.1.0.1:

• Deconfigure Oracle Restart 12.1.0.1

  • # cd /u01/app/12.1.0.1/grid/crs/install
    # /u01/app/12.1.0.1/grid/perl/bin/perl /u01/app/12.1.0.1/grid/crs/install/roothas.pl -deconfig

Regarding ASM backwards compatibility please be aware that changing the COMPATIBLE attributes within ASM will get you in trouble – see the Oracle Database Upgrade Guide for further information:
http://docs.oracle.com/database/121/UPGRD/afterup.htm#CEGJDCDD

–Mike

PS: See bug18160024 or the GI install guide, section A11.4 for the Standalone GI downgrade instructions from 12.1.0.2.0.