System Administrator’s Guide U42252-J-Z915-1-76

Introduction The Database Backup
Figure 2: Logical database structure
2.3 The Database Backup
Every recovery procedure depends on a correctly performed database backup,
which consists of copies of the database files being made at operating system
level and transferred to an external storage medium or created as a NAS
snapshot. These copies depict a state that is not identical to the current one.
In the case of one or more database files being lost, the backup copies serve
as the starting time for a required recovery. During any recovery, all redolog files
accruing since the backup are reapplied, thus updating from the backup to the
current status.
2.4 Archive Mode of the Database
To ensure that all the redolog files accruing since the backup are available, the
database must be operated in ARCHIVELOG mode, which makes sure that
redolog files are not overwritten unless they have first been archived on a
separate disk area (archive directory) by ORACLE’s archiving function (see
figure 3).
control file
USER
database files
redolog files
SYSTEM TEMP
Tablespaces