Multiplexing redo log files
Oracle uses specific terminology in describing the management of redo logs. Each Oracle instance records the changes it makes to the database in redo logs. You can have one or more redo logs, referred to as redo log members, in a redo log group.
Logically, you can think of a redo log group as a single redo log file. However, Oracle allows you to specify multiple copies of a redo log to protect the log against media failure. Multiple copies of the same log are grouped together in a redo log group. All redo log groups for an instance are referred to as a redo thread.
There are ways you can rebuild the static part of the control file if you lose it, but there is no way to reproduce a lost redo log file; be sure that you have multiple copies of the redo file.