There are two types of backup, physical and logical. A physical backup operation results in a byte-for-byte copy of the Oracle database files.
Physical backup is also called Operating System backup (O/S) because the DBA copies the files using the O/S, not Oracle.
Logical backup is created using the EXP utility. This utility completely reorganizes the data by extracting it from the physical database file(s) and putting it in a single,
"flat" operating system file. The logical backup process is not part of this course.
The images below illustrate the concept for these two types of backup.
A complete physical backup includes all the important parts of a database: control file(s), redo log files, archive log files, and datafiles. If
the original data is lost, these file copies can be recovered because the backup contains all the necessary information. In the case ofmedia
, a physical database backup is the best possible way to successfully recover the data. Without a copy of the database files, not only
must the database be re-created empty of user objects, the objects themselves must be re-created. Additionally, all user data must be re-entered.
When you make a physical backup of a database, you actually take an operating system
backup of datafiles while the database is open or closed. An
operating system (O/S) backup is made using an operating system command and can be written to disk or tape in any format that a specific
operating system supports.
DBAs usually consider logical backup
a supplement to their database backup strategy because the EXP utility can be very time-consuming;
imagine doing 100 million inserts when the database is large. The EXP utility does not provide the same speed advantages that O/S backups offer at recovery time.
The next lesson examines the available options for database backup.