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The parameter required for checkpointing since 9i is FSMMT and from 10.2 onwards, if it is set to a non-zero value, it would be automatically tuned by Oracle. As long as you are not hitting the checkpoint not complete wait event, you are most probably okay. Also, if you would set the FSMMT , Oracle offers a redo log file size advisor which can help in finding the right size of the redo log for your db.
Just my 2 cents.
Look in your alert log to see how long it is between redo switches during times of heavy usage. Multiply the size of the redo by how much it would take to switch every 30 minutes. For example, if you switch every 5 minutes, multiply by 6. Then make them much larger and rely on the 1800 second timeout (or better, do the figuring during maximal loading or batch update times). Let it run a few days then check the advisor as in http://docs.oracle.com/cd/E25178_01/server.1111/e16638/build_db.htm#autoId3
Here's the proper way to figure FSMT http://docs.oracle.com/cd/E25178_01/server.1111/e16638/instance_tune.htm#PFGRF13015
Don't bother changing dbw settings yet. Wait until you see some evidence you need to do that.