Despite the prevalence of redundant or protected disk storage, media failures can and do occur. In cases in which one or more Oracle datafiles are lost due to disk failure, you must use database backups to recover the lost data.
There are times when simple human or machine error can also lead to the loss of data, just as a media failure can. For example, an administrator may accidentally delete a datafile, or an I/O subsystem may malfunction, corrupting data on the disks. The key to being prepared to handle these types of disasters is implementing a good backup and recovery strategy.
Proper development, documentation, and testing of your backup and recovery strategy is one of the most important activities in implementing an Oracle database. You must test every phase of the backup and recovery process to ensure that the entire process works, because once a disaster hits the complete recovery process must work flawlessly.
Some companies test the backup procedure but fail to actually test recovery using the backups taken. Only when a failure requires the use of the backups do companies discover that the backups in place were unusable for some reason. It’s critical to test the entire cycle from backup through restore and recovery.
Two basic types of backups are available with Oracle:
The datafiles for one or more tablespaces are backed up while the database is active.