Oracle7 Server Administrator's Guide
Guidelines for Control Files
This section describes guidelines you can use to manage the control files for a database, and includes the following topics:
Name Control Files
Assign control file names via the CONTROL_FILES initialization parameter in the database's parameter file. CONTROL_FILES indicates one or more names of control files, separated by commas. The instance startup procedure recognizes and opens all the listed files. The instance maintains all listed control files during database operation.
During database operation, Oracle7 Server writes to all necessary files listed for the CONTROL_FILES parameter.
Multiplex Control Files on Different Disks
Every Oracle7 database should have at least two control files, each stored on a different disk. If a control file is damaged due to a disk failure, the associated instance must be shut down. Once the disk drive is repaired, the damaged control file can be restored using an intact copy of the control file and the instance can be restarted; no media recovery is required.
Behavior of Multiplexed Control Files
The following list describes the behavior of multiplexed control files:
- Two or more filenames are listed for the initialization parameter CONTROL_FILES in the database's parameter file.
- The first file listed in the CONTROL_FILES parameter is the only file read by the Oracle7 Server during database operation.
- If any of the control files become unavailable during database operation, the instance becomes inoperable and should be aborted.
The only disadvantage of having multiple control files is that all operations that update the control files (such as adding a datafile or checkpointing the database) can take slightly longer. However, this difference is usually insignificant (especially for operating systems that can perform multiple, concurrent writes) and does not justify using only a single control file.
Attention: Oracle strongly recommends that your database has a minimum of two control files on different disks.
Place Control Files Appropriately
Each copy of a control file should be stored on a different disk drive. Furthermore, a control file copy should be stored on every disk drive that stores members of online redo log groups, if the online redo log is multiplexed. By storing control files in these locations, you minimize the risk that all control files and all groups of the online redo log will be lost in a single disk failure.
Manage the Size of Control Files
The main determinants of a control file's size are the values set for the MAXDATAFILES, MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, and MAXINSTANCES parameters in the CREATE DATABASE statement that created the associated database. Increasing the values of these parameters increases the size of a control file of the associated database.
See Also: The maximum control file size is operating system-specific. See your operating system-specific Oracle documentation for more information.