Redo log files are multiplexed in your database. The disk in which you have one of the redo log members is highly fragmented. In the process of defragmentation you lose the redo log member, which is…

SMON handles instance recovery and free-space coalescing but has no ability to automatically detect or recreate lost redo log member files.

A full database restore is unnecessary because the lost member's content is preserved in the other surviving members of the same multiplexed group.

Restoring from a full backup is not required since identical data exists in the remaining members of the same redo log group, making a backup restore redundant.

Flashback technology uses Flashback Logs to rewind database state to a prior SCN, but it cannot recreate or restore physical redo log member files.

RMAN can restore archived redo logs and datafiles from backup, but it cannot restore or recreate individual online redo log member files from a standard backup set.

In a multiplexed redo log setup, Oracle writes simultaneously to every member of a group, making all members byte-for-byte identical. Because the lost member belongs to a non-current group, no active writes are occurring to it, so copying any intact surviving member from the same group to the missing file location fully restores the data. After the copy, the database can be informed of the updated member path using ALTER DATABASE if needed.