For an Oracle DBA who has been working on non-RAC databases for a while, when asked to work on a RAC database even if the DBA has hands-on experience with RAC and its concepts, it takes a shift in mindset to administer a RAC database.
Basic tasks that were second nature in non-RAC becomes a bit different in RAC.
For example, if the DBA has to
- convert the database to [NO]ARCHIVELOG mode
- recover SYSTEM tablespace due to media failure
then the instance needs to be mounted with the parameter CLUSTER_DATABASE flipped to FALSE. After performing the desired operation, the instances would need to bounced with the parameter set to TRUE. Essentially, the database is turned into a single instance database; after performing the desired operation, it is started in clustered mode.
This in contrast to a non-RAC database where you just shutdown/startup mount the database and do the the desired operation.
Well… this is just a small example to demonstrate the need for the RAC mindset… 
