In an Oracle Data Guard configuration, the primary and standby databases can have different configurations. It’s very common to have a smaller server for the standby database (less CPUs, less memory, etc.) and it’s quite trivial to configure. But what about RAC?
Even after years of working with something, you can always learn new stuff. Today I tried to create a standby database using the duplicate command. When you duplicate a database you need to connect to both instances (primary as target and standby as auxiliary) using SQL*Net (and not “/”). Since the standby is in nomount, the listener blocks connections to it, so when trying to connect to it using the listener we get “ORA-12528: TNS:listener: all appropriate instances are blocking new connections”.