Oracle records database changes in its redo logs.
When Data Guard is activated, these changes are shipped from the primary to the standby and applied there.
This keeps the two databases synchronized with a time lag dependent on how often the changes are shipped and how long it takes to ship them.
ODG Standby Database Types
Physical Standby
Logical Standby
ODG – Available Modes
Mode
=Maximum protection (LGWR, SYNC, AFFIRM)
highest level of protection
no data loss
primary stops if redo data cannot be applied to the standby
=Maximum availability (LGWR, SYNC, AFFIRM)
high level of protection
minimal data loss
switches to maximum performance mode if standby unavailable
automated catch-up of gaps if redo was not able to be written
=Maximum performance (LGWR|ARCH, SYNC|ASYNC, AFFIRM|NOAFFIRM)
medium level of protection
some data loss
primary not affected by standby unavailability
General objectives of DR system :
Recovery Point Objective (RPO) = no more than X minutes of data loss
Recovery Time Objective (RTO) = Y hours from declaration of disaster
where X and Y are chosen by Project Build Team
With tape based DR, tapes need to be shipped to DR site. Tapes can be lost or damaged with problems identified too late. ODG will know when a redo log is missing or damaged at the point when it is to be applied to the standby not when the disaster has already occurred.
ODG Implementation Overview :
Configure required parameters on Primary and Secondary DB in init<SID>.ora or spfile as per Oracle online documentation - Data Guard
Concepts and Administration.
ODG Activation Overview
Once all ODG parameters are set, on the PRIMARY DB:
sqlplus / as sysdba
SQL> alter system set log_archive_dest_state_2=‘ENABLE';
SQL> show parameter log_archive_dest_state_2
Deactivate via:
sqlplus / as sysdba
SQL> alter system set log_archive_dest_state_2=‘DEFER';
SQL> show parameter log_archive_dest_state_2
ODG Troubleshooting
Database alert logs
ST04N
Alerts from OS level
Solution Manger
Oracle tools
Database alert logs
Oracle Alert Logs can be found in $SAPDATA_HOME/saptrace/background on both Primary database and Standby database.View the logs to check for messages / errors:
Standby Database Backups
Disaster Recovery: High Level Overview
ODG Support: Common Problems
The following problems can occur :
Problem: logs missing / not received
Problem: Redo logs not being applied
Problem: Can not allocate log
Problem: Redo storage full / filling
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.
User | Count |
---|---|
7 | |
5 | |
5 | |
5 | |
5 | |
4 | |
4 | |
4 | |
3 | |
3 |