Oracle RMAN 11g Backup and Recovery- P2: Oracle, yet another edition of our RMAN backup and recovery book has hit the shelves! Oracle Database 11g has proven to be quite the release to be sure. RMAN has new functionality and whizbang new features that improve an already awesome product. RMAN has certainly evolved over the years, as anyone who started working with it in Oracle version 8 can attest to. | 18 Part I Getting Started with RMAN in Oracle Database 11g Inactive This is an online redo log that isn t active and has been archived. Unused Th is is an online redo log that has yet to be used by the Oracle database. The status of an online redo log group can be seen by querying the V LOG view as seen here SQL select group status from v Log GROUP STATUS 1 INACTIVE 2 INACTIVE 3 INACTIVE 4 CURRENT Multiplexing Online Redo Logs If you want to have a really bad day then just try losing your active online redo log. If you do it s pretty likely that your database is about to come crashing down and that you will have experienced some data loss. This is because recovery to the point of failure in an Oracle database is dependent on the availability of the online redo log. As you can see the online redo log makes the database vulnerable to loss of a disk device mistaken administrative delete commands or other kinds of errors. To address this concern you can create mirrors of each online redo log. When you have created more than one copy of an online redo log the group that log is a member of is called a multiplexed online redo log group. Typically these multiplexed copies are put on different physical devices to provide additional protection for the online redo log groups. For highest availability we recommend that you separate the members of each online redo log group onto different disk devices different everything. Here is an example of creating a multiplexed online redo log group alter database add logfile group 4 C ORACLE ORADATA BETA1 C ORACLE ORADATA BETA1 size 100m reuse Each member of a multiplexed online redo log group is written to in parallel and having multiple members in each group rarely causes performance problems. The Log Sequence Number As each online redo log group is written to that group is assigned a number. This is the log sequence number. The first log sequence number for a new database is always 1. As the online redo log .
