As I??™ve emphasized throughout this
book, the need for cold backups is minimized or eliminated if you use RMAN; your database may
never need to be shut down for a cold backup (unless disaster strikes??”in which case, be sure to
create a RAC database as well!).
Implementing Online Backups
Consistent offline backups can only be performed while the database is shut down. However, you
can perform physical file backups of a database while the database is open, provided the database
is running in ARCHIVELOG mode and the backup is performed correctly. These backups are
referred to as online backups.
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412 Oracle Database 11g DBA Handbook
Oracle writes to the online redo log files in a cyclical fashion: After filling the first log file, it
begins writing to the second, until that one fills, and it then begins writing to the third. Once the
last online redo log file is filled, the LGWR (Log Writer) background process begins to overwrite
the contents of the first redo log file.
When Oracle is run in ARCHIVELOG mode, the ARCH background process makes a copy of
each redo log file after the LGWR process finishes writing to it. These archived redo log files are
usually written to a disk device. They may instead be written directly to a tape device, but this
tends to be very operator intensive.
Getting Started
To make use of the ARCHIVELOG capability, you must first place the database in ARCHIVELOG
mode.
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