Overview of Data Guard

Overview of Data Guard:

In Today’s world Data availability is most important for any business. Most of the business running in multiple countries and location and different timezone.it this case for running the business 24/7 data should be available. Oracle provide the Solution software called “DATAGUARD” for minimizing the downtime and maintenance. It Aids in establishing and maintaining a secondary ”standby Database”.

Today Business Requirements:

1:  data availibity on 24/7.

2: High Availability like minimize schedule downtime and unscheduled downtime.

3. Disaster recovery protection.

4: Minimize the Cost

Data Guard’s Evolution

Oracle introduced the standby concept in Oracle Database 7.3. But this version of standby supported only disaster recovery solution and this standby Database could not be opened in read only mode.In Oracle Database 7.3, the DBA has to manually transfer the log from Primary to standby .in the event of Primary Database failure. The loss of current redo logs means loss of data.Oracle introduced automatic redo transport service in oracle 8i. This reduced the manual interventions by DBA’s & in Oracle 9i this standby Technology renamed as ORACLE DATA GUARD.

Data Guard’s Features:

• Ø    Oracle provide data guard as a Bundled feature in the “Enterprise Edition” only.
• Ø  Oracle Data guard provides High Availability and replication and data protection and disaster recovery for enterprise data.
• Ø  Oracle Data guard provides a set of services that create, maintain, manage and monitor one or more standby Database to enable production Database to survive disaster and data corruption.
• Ø  Data guard maintain this standby databases as a copies of the production Database.
• Ø  If the Production Database become unavailable because of planned or unplanned outage, so data guard can switch any standby Database the production role, minimizing the downtime associated with outage.

Following are the different benefits in using Oracle Data Guard feature in your environment.

Ø    Oracle Data Guard Provides a combined solution of High Availability and disaster recovery using standby Database without compromising the Primary Database performance.

Ø    It supports heterogeneous configurations in which the Primary and standby systems may have different CPU architectures, operating systems (for example, Microsoft Windows and Linux), operating-           system binaries (32-bit/64-bit), or Oracle Database binaries (32-bit/64-bit)

Ø    Offloading Backup operation to standby Database.

Ø    Automatic Gap detection and Resolution in standby Database.

Ø    Automatic Role Transition using Data Guard Broker.

Data Guard Architecture:

                   

• Ø  Data guard Configuration Consist of one production Database and one or more standby Database. The Database in the DG configuration are connected by oracle NET service.
• Ø  There are no restriction on where the Database are located provided they can communicate with each other.
• Ø  A standby database is created from the backup of primary database .backup database files and control files are transferred to standby site.
• Ø  One of the main requirements of the data guard is primary database should run on ARCHIVELOG mode. This ensure the all the changes made to primary database are captured and kept in archive redo log files.
• Ø  Primary and standby Database is connected through Net connection to facilitate the transfer of archive redo logs.
• Ø  Standby Database receives transaction details from Primary Database using archive redo logs.
• Ø  Standby Database can be open in read-only mode or recovery mode.in recovery mode transaction receive from Primary Database applied on standby Database to keep synchronized with Primary Database.
• Ø  In standby read only mode is used for reporting purpose.in read only mode log are transfer service is continue but log apply service is stop.
• Ø  We can manage Primary and standby Database using SQL CLI or DG broker interface and GUI that is OEM.

Figure 1-1 illustrates the basic working of data guard. The diagram shows the flow of working of data guard environment. In above diagram our primary database is located in India and standby database is remotely located in USA for disaster recovery. The primary and standby database is connected through Oracle Net Service. The client application access the primary database and update the data. The archiver process copies the changes redo logs archive to local archive destination. After copying the archiver logs oracle transfer the archive log to standby site using log transport service. This log transfer process transfers the archive redo log file to standby site. On standby site data guard provide the log apply process for applying the redo records from the archived log files.