Configuration doubt

Question

Could somebody, please, explain me ?
I know tha when I set up redo shipping, the number of standby redolog (at standby database) must be at less, one more than the number of online redolog present in the source database. That is why when the standby database is a single instance I execute the following, at the standby database, if the number of online redolog in the source is 2:
ALTER DATABASE ADD STANDBY LOGFILE GROUP 4 ('+BD2')SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE GROUP 5 ('+BD2') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE GROUP 6 ('+BD2') SIZE 50M;
After, I set the LOG_ARCHIVE_DEST_2 parameter like
alter system set LOG_ARCHIVE_DEST_2='LOCATION=+BD3/ VALID_FOR=(STANDBY_LOGFILE,PRIMARY_ROLE)';
BUT when I have a Real Application Clusters with two instances as standby database, I need create the standby redolog in both instances or just in one ? :
INSTANCE1
ALTER DATABASE ADD STANDBY LOGFILE GROUP 4 ('+BD2')SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE GROUP 5 ('+BD2') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE GROUP 6 ('+BD2') SIZE 50M;
INSTANCE2
ALTER DATABASE ADD STANDBY LOGFILE GROUP 4 ('+BD2')SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE GROUP 5 ('+BD2') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE GROUP 6 ('+BD2') SIZE 50M;
Thanks you so much.

Answer 1

Thanks Cow Town but it is not my point. I say when the primary is a single instance and I want to have an standby in a RAC compose of two instance. That is:
source database-: single instances
future standby database: two instances RAC
As said I know that if the future standby database will be a single instance too, I need to create one standby group more than the number of online redolog present in the source DB. But in my situation the standby will be two instances RAC and my question is if I need to create the four groups in each instance or just in one of all.
Please tell me if you understand my question, and again thanks so much.