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Overview of RAC Backup and Recovery

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%.


Believe it or not, other than a few quirks which will be covered in detail, RAC backup and recovery is identical to almost all other Oracle database backup and recovery operations. At the basic level, after all, it is only a single Oracle Database 10g database being backed up.

In most cases, an instance failure will be recovered by other RAC instances. Special cases of instance failure will be covered at the end of this chapter.

The quirks come into play when dealing with a RAC database that uses archive logging. Archive logging introduces an added layer of complexity, due to the requirement that all archive logs from all instances in the RAC environment must be backed up. Luckily, Oracle Database 10g allows the database to archive log to more than one destination, and with a little ingenuity on the DBA?s part, all archive logs can be available for recovery at all times.

Oracle Database 10g RAC offers a multitude of backup possibilities:

* Export

* Cold backup using scripts

* Hot backup using scripts

* RMAN backup with a catalog

* RMAN backup without a catalog

* The use of third party tools to perform backup and restore operations

As detailed in the following sections, each of these options has its good and bad qualities.

Export

A database export is a logical copy of the structure and data contained in an Oracle database. Archive log information cannot be applied against a database recovered using the import of an export file. This means that an export is a point-in-time copy of a database. In this way, an export is like a cold backup of a database that is not in ARCHIVELOG mode.

Exports are useful in that they allow easy restoration of tables and other structures, instead of having to bring back entire tablespaces, as would be required with most other forms of backup and recovery. The import process can also be used to rebuild tables and indexes into more optimal configurations or to place data into new locations. Another benefit is that exports are capable of being copied across platforms. For example, an export from a WIN2K server can be copied to a Solaris server and applied there.

The drawbacks to exports are that they take a great deal of time to generate depending on database size.  They can only be performed against a running database, and they take a long time to recover, again based on database size. In some versions of Oracle, there are also file size limitations.

Cold Backup Using Scripts

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.


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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