How many groups of standby redo log is reasonable?
In the case of a single machine
All redo_log groups +1
RAC environment
All redo log Number of groups + Number of instances
Normally, the number of redo log groups in each instance is the same. For example, for you, the number of standby redo log groups is (n+1)*thread.
If there are three instances of rac, each instance is 3 log groups, then if you want to do the standby log of dg, you need to add 12 standby log groups.
(3+1)*3=12
If there are three instances of rac, instance 1 has three log groups, instance 2 has four log groups, instance 3 has five log groups, and there are 12 log groups in total, then if you want to do the standby log of dg, you need to add 15 standby log groups.
All redo log groups + instances =(3+4+5)+3 = 15
