Configuring data guard: how many standby redolog do I need?

Question

Hi all, I want to add a standby databse to my RAC test environment but I don't understanad how many redolog I need.
The main db is a 2 node RAC (10.2.0.4.0); every node has 3 log groups; every log group has 2 logfile (every log group is multiplexed on DG_DATA1/ASR/ and FLASH_RECOVERY_AREA/ASR/ )
The standby db will have all its datafile on the same filesystem, so I already configured the trasnslations parameters:
DB_FILE_NAME_CONVERT='/opt/oracle/app/oracle/oradata1/ASRSB','+DG_DATA1/ASR','/opt/oracle/app/oracle/oradata2/ASRSB','+FLASH_RECOVERY_AREA/ASR'
LOG_FILE_NAME_CONVERT='/opt/oracle/app/oracle/oradata1/ASRSB','+DG_DATA1/ASR','/opt/oracle/app/oracle/oradata2/ASRSB','+FLASH_RECOVERY_AREA/ASR'
Replication via rman works well, but I have to manually add the standby redolog on the standby db and which formula to use to calculate the number of the standby redolog needed. Which is the correct formula between :
1)
# of standby log = ( # of redolog files + 1) * # of thread = (6 +1)*2 = 14 standby redolog files
2)
# of standby log = ( # of redolog groups + 1) * # of thread = (3 +1)*2 = 8 standby redolog files
thanks,
andrea

Answer 1

Andrea,
I think 8 should be the answer on your question. Because you have 3 log groups and 2 threads therefore (3+1)*2 = 8.
According to the documentation :
http://download.oracle.com/docs/cd/B19306_01/server.102/b14239/create_ps.htm#SBYDB00426
Minimally, the configuration should have one more standby redo log file group than the number of online redo log file groups on the primary database. However, the recommended number of standby redo log file groups is dependent on the number of threads on the primary database. Use the following equation to determine an appropriate number of standby redo log file groups:
(maximum number of logfiles for each thread + 1) * maximum number of threads
I think you may get confused with maximum number of logfiles. But sometimes logfile is used as a synonym to log group. The actual log group files are usually called log members. (for instance MAXLOGFILES parameter specifies the maximum number of log groups and MAXLOGMEMBERS specifies the maximum number of members for each group).
Each additional member in a redo log group is just a multiplexed copy. You can also consider multiplexing the standby redo log files, the same why you do for redo log members.
In order to learn more about the usage, benefits and limitations of Standby Redo Logs (SRL) you can refer to Metalink Note 2193444.1.
I hope this helps.
--Mihajlo