Redo log files record all changes made to the data. Every Oracle database has a set of two or more redo log files . The set of redo log files is collectively known as the redo log for the database. A redo log is made up of redo entries (also called redo records ).In the event of file corruption or disk failure, the DBA can restore datafiles from a backup copy, and then apply the changes listed in the redo log to bring the backup datafiles up to date.
Redo log contains one or more copies of itself in case one of the copies becomes corrupt or is lost due to a hardware failure. Collectively, these sets of redo logs are referred to as redo log groups. Each multiplexed file within the group is called a redo log group member.
Each database must have a minimum of two redo log groups because redo logs are used in a circular fashion.
