Oracle Database 11g Oracle Real Application Clusters Handbook, 2nd Edition, 2nd Edition

Administering Online Redo Logs

Oracle uses online redo log files to log any changes to data blocks. Each instance has its own set of online redo log files. A set of redo logs used in a circular manner by an instance is known as a thread. A thread contains at least two online redo logs. The size of an online redo log is independent of other instances’ redo log sizes and is determined by the local instance’s workload and backup and recovery considerations.

Each instance has exclusive write access to its own online redo log files. An instance can read another instance’s current online redo log file to perform instance recovery if that instance has terminated abnormally. Thus, an online redo log needs to be located on a shared storage device and ...