Every ORACLE database has one or more physical data files. A databases data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database.
A data file can be associated with only one database.Once created a data file cant change size.
The set of Redo Log files for a database is collectively known as the databases redo log.
The Primary function of the redo log is to record all changes made to data.
The Information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a databases data files.