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Oracle Data Control Files

Data in control files and initialization files


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Data types

Control Files

A database should have at least two copies of the control file on different physical disks. Without a current copy of the control file, you run the risk of losing track of portions of your database. Losing control files is not necessarily fatal and there are ways to rebuild them. However, rebuilding control files can be difficult, introduces risk, and can be easily avoided. The location of the control files is defined, as previously mentioned, by the
CONTROL_FILES 

initialization parameter. You can specify multiple copies of control files by indicating multiple locations in the CONTROL_FILES parameter for the instance, as illustrated here:
control_files = (/u00/oradata/control.001.dbf,
/u01/oradata/control.002.dbf,
/u02/oradata/control.003.dbf)

This parameter tells the instance where to find the control files. Oracle will ensure that all copies of the control file are kept in sync so all updates to the control files will occur at the same time. If you do not specify this parameter, Oracle will create a control file using a default filename or by leveraging Oracle Managed Files (if enabled). Many Oracle Databases are deployed on some type of redundant disk solution such as RAID-1 or RAID-5 to avoid data loss when a disk fails. You might conclude that storing the control file on protected disk storage eliminates the need for maintaining multiple copies of control files and that losing a disk will not mean loss of the control file. But there are two reasons why this is not an appropriate conclusion.