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Cold Backup Using Scripts

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.


Cold backup using scripts can backup an Oracle Database 10g RAC database whether it is in ARCHIVELOG mode or not. A cold backup means that the database is shutdown, and all files are backed up via a manually created script.

Generally speaking, the DBA can always recover from a cold backup unless something happens to the backup media or files. However, unless the database is in ARCHIVELOG mode, a cold backup is a point-in-time backup. If a database is archive logging, which means that all filled redo logs are copied to an archive log before being reused, the cold backup can be restored to the server and archive logs applied to make the database as nearly current as possible.

The drawbacks to cold backups are that the database must be shutdown in order to perform a cold backup, a cold backup can take a long period of time depending on database size, and the DBA has to manually maintain the backup scripts. Another problem is that cold backup on raw partitions on UNIX or Linux involves the command dd. Cold backup, by its very nature, defeats the purpose of a high availability 24x7 RAC database solution.

Hot Backup Using Scripts

A hot backup is taken while the database is operating. A special command places the database?s tablespaces into BACKUP mode, which copies live files. Once the copy operation in a hot backup is complete, the datafiles are taken out of BACKUP mode.

In order to use hot backup, the database must be in ARCHIVELOG mode. Once the datafiles are copied, the archive logs that were generated while the datafiles were in BACKUP mode are also copied to the backup location. The datafile backups and the archive logs are then used to recover the database to the exact state it was in at the end of the backup.

Once the backup is complete, any subsequent archive logs can be applied in order to recover to any point in time between the backup and the last available archive log.

As mentioned, the database is active and in use during a hot backup. This allows a 24X7 shop to operate without having to shut down to backup the database.

Drawbacks of the hot backup include:

* Database performance can degrade during the backup.

* All archive logs generated during the backup process must be captured.

* The scripting for a hot backup can be quite complex.

A Few Words on Using Manual Scripts

Manual scripts should be generated using SQL and PL/SQL routines against the data dictionary of an operating database. This allows the addition of a tablespace or a change in an archive log destination to be automatically engineered into the script. Most attempts to manually maintain backup scripts ultimately end in disaster, as a DBA misses a new tablespace or other structural element and thus, it is not backed up.

In RAC, the gv$ and dba_ series of views should be used to create dynamically generated cold and hot backup scripts. Examples of hot and cold backup script generators are available on the Rampant website, using the username and password provided with this book. These scripts have been tested under WIN2K and UNIX environments, but they should be thoroughly tested on the DBA?s own system before they are fully relied upon.

 


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.

http://www.rampant-books.com/book_2004_1_10g_grid.htm


 

 
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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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