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 Oracle RAC Backup and Recovery
Oracle Tips by Burleson Consulting

Oracle 11g Grid & Real Application Clusters by Rampant TechPress is written by four of the top Oracle database experts (Steve Karam, Bryan Jones, Mike Ault and Madhu Tumma).  The following is an excerpt from the book.

Backup and Recovery

One common misconception about Oracle RAC is that it provides all the backup necessary because multiple nodes are in use.  However, it is important to remember that this redundancy is only at the instance level, not the database level. This means that if a failure occurs at the database level, such as lost or corrupt datafiles, RAC will not be able to keep the system online by itself.

 

There are two types of failure that must be considered:

  • Database Failure is caused by a loss or corruption at the file level.  Remember that while instances are redundant, database files are not.

  • Instance Failure is caused when an instance crashes.  In a RAC environment, the other instances in the cluster can continue to work, and the instance will recover itself when the system comes back online.

RAC Backup and Recovery

While RAC is a complex system involving multiple machines plugging into a centralized database, backup of the environment is relatively simple.  The same basic tools or commands that are used to backup a single instance database can, in most cases, back up a RAC database.

 

A RAC database has one single set of datafiles and control files with redo log groups for each instance.  All of these files are centralized, as RAC requires shared storage in order to run.  Backing up those centralized files is the same as backing up files for a single instance, except that there will be a few more files.

 

A DBA can use many methods to backup his RAC database.  These methods include:

  • Logical export via exp or the Datapump tool expdp

  • User-created cold or hot backups

  • RMAN backups (hot or cold)

Before these backup options can be explored, it is important to understand how RAC and backups come together to form a complete redundancy solution.

Maximum Availability Architecture (MAA)

Oracle recommends a standard known as the Maximum Availability Architecture, or MAA.  This plan provides contingencies both at the instance level and the database level.

High Availability (HA)

Generally speaking, instance level redundancy is known as High Availability (HA).  This means that if an instance is lost in a RAC cluster, the high availability features ensure that other instances will take over the workload as seamlessly as possible.  HA does not cover datafile loss or corruption.  Instead, it only covers the runtime components of the Oracle environment.

 

High availability can be achieved in a RAC environment when proper failover techniques are used, such as Transparent Application Failover (TAF) and/or Fast Connect Failover (FCF).  Though an instance failure will require reconfiguration, i.e. instance recovery of the lost instance, the basic components of RAC should still be available.

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