Oracle 11.2.0.4 order of upgrade discussion

Question

Hi all:
We have Oracle DB 11.2.0.3 on IBM AIX (power system, os level 4, 64bit), need to upgrade it to 11.2.0.4 and apply CPUJAN2015 patch.
We already complete upgrade in UAT, and prepare for Prod in client site. UAT OS directory set up is: home_1 (11.2.0.3), home_2 (11.2.0.4).
Due to serious client's request, we need to keep 'home_1' always for latest oracle version, so need to rename home_2 to home_1 after upgrade.  Client and us are discussing the 'order-of-upgrade' due to directory rename.  Our approach is:
originally,  server has 'home_1' 11.2.0.3 and 'home_2' .  Take backup of 'home_1' oracle binaries, RMAN backup DB.
Start upgrade process -
1. install 11.2.0.4 to 'home_2'. [use guidelines in 11.2.0.4 oracle installation by OUI]
2. cd to 'home_2'/dbs, open DB by 'home_2/dbs/bin/sqlplus (sure we use correct configuration files like initSID.ora and tns files, etc):
      sqlplus > startup upgrade;
    >@catupgrad.sql; exit;
      sqlplus > startup
                    >@utlu112s.sql; @catuppst.sql; @utlrp.sql;
3. shutdown/startup DB based on necessary
4. apply CPUJAN2015 patch. [use guidelines in README file in patch "p20132517_112040_aix64"]
5. shutdown/startup DB and listener based on necessary.
we rename 'home_1' (11.2.0.3) -> 'home_1bkup' (11.2.0.3), 'home_2' (11.2.0.4) -> 'home_1' (11.2.0.4).  So next upgrade we'll install new version in 'home_2' again, and start same process.  This way saves us from renaming many server scripts/application code which point to 'home_1'.
Our client suggested approach-
1) Backup database instance (RMAN) or  (file copy when database is shutdown down) in 11.2.0.3. 
2) Install 11.2.0.4 in HOME_2
3) Move HOME_2 to HOME_1 (the original home of 11.2.0.3)
4) Start up database instance in upgrade mode and upgrade the database to the 11.2.0.4
5) ( may need to do some shutdown startup to ensure it is working fine).
6) Completed?
7) Shutdown database instance
8) Move HOME_1 to HOME_2 (the original home of 11.2.0.4)
9) Oracle CPU patch apply
10) Move HOME_2 to HOME_1 (the original home of 11.2.0.3)
11) Start up database instance in and update cpu to the database
12) Backup database instance (RMAN) or  (file copy when database is shutdown down) in 11.2.0.4. 
This will ensure at all time, we are following Oracle’s ‘model’ upgrade path.
I feel step 8 & 10 moving is unnecessary, can't we stay the same oracle home, 'home_2' (11.2.0.4) in our approach, and apply CPU patch at DB? Client argues is 'for all time we following oracle's model upgrade path',  what is 'model upgrade'?  is any Doc ID for it?  we don't want to unnecessary moving oracle home too many times - that is risky and many cause potention problem.
3rd enhanced approach we have so far -
1) Backup database instance & oracle binaries in 11.2.0.3 HOME_1 to 'HOME_1bkup'. 
2) Install 11.2.0.4 in HOME_2
3) In HOME_2, start up database instance in upgrade mode, upgrade & apply CPU to database in our previous procedure.
4) ( may need to do some shutdown startup to ensure it is working fine).
5) Completed?
6) Shutdown database instance in HOME_2
7) Backup database instance (copy datafile over os) & oracle binaries in 11.2.0.4 HOME_2 to 'HOME_2bkup'.
8) Move HOME_2 to HOME_1
9) Start up database instance in HOME_1 (11.2.0.4).
This way has backups for 11.2.0.3 and 11.2.0.4.
Can anyone take a look and let us know any important error or missing steps in the above, especially the 3rd approach?
thank you very much!!     

Answer 1

Using new ORACLE_HOME is one of the best practice to reduce the downtime required for upgrade since new home can be created independent of actual downtime.
in other words, you can install new binaries in new home without impacting existing DB. During the upgrade, all you need to do is point the instance to new home and perform the DB upgrade. This method also helps in quick rollback since you have original ORACLE_HOME intact. One more  benefit is that you don't need to take separate ORACLE_HOME backup since you already have everything.
There is no need of following this approach for CPU patching since it is very simple to rollback failed CPU patch.
Please remember, changing oracle_home directory might require you to do relinking so it is recommended to perform this on some non-prod system first.
Hope it helps.
Thanks,
Abhi