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Redo log file problems

Expert Brian Peasland explains why it is important to make sure online redo logs are multiplexed.

My database was abruptly shut down (I don't know why). While we were opening the database it was showing the error in log files, so we tried to add a new redo log file for the existing group. It was added, and we are not able to switch the database because we are at mount stage, and even when we use the command to clear the logfile with "alter database clear unarchived logfile group 4," it is not clearing the group and the database is not switching. At mount stage, the database is in hang position. The database will open if we drop that redolog file offline, but we will lose some data. To overcome from these types of errors, what precautions should we take at this moment?
The first thing to do in the future is to make sure that the online redo logs are multiplexed. If one redo log file becomes corrupt, Oracle can use the other one. The multiplexed online redo log files should be on separate disk devices.

If you are still unable to open your database, you can try to open the database with the RESETLOGS option. This will clear out all online redo log files. You may experience loss of some transactions, so this should be a last option. But this may also be your only option, too.

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