Redo logs. Please explain.

I'm trying to learn the DBA job by reading the Oracle manuals. Can someone please explain how the redo log files relate to one another? If I create a database with the following redo log groups....

CREATE DATABASE "tardis"
...
LOGFILE GROUP 1 ('a.log', 'b.log') size 1m, LOGFILE GROUP 2 ('c.log', 'd.log') size 1m;

Which files are mirrors of which? And which are used in the circular fashion as described in the concepts manual?

Do 'a' and 'c' mirror each other, or do 'a' and 'b'? I need to know so I know which drives to place the files on to protect against media failure.

The manuals seem to cover everything about redo logs except this.

--
Chuck Hamilton
chuckh_at_ix.netcom.com

Never share a foxhole with anyone braver than yourself!