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Is Oracle Data Guard really a Disaster Recovery solution? I thought Data Guard uses the Oracle Standby database technology, and as the standby database uses the Archived redo logs files, it will always 'lag' behind the production database. Also, if the production database 'crashed' you could loose transactions, OR am I missing something in Oracle Data Guard?
Yes, you are missing something. Data Guard is not simply a new marketing name for former Standby Database, it trully is a new concept. You are wrong in assuming that a standby database uses only archived redo logs as a mean of transporting changes from primary to the standby - with Data Guard there is a new concepts of Standby online redo logs, to which changes might be written simultaneously with those on primary side.
Depending on which Data Guard configuration you choose and on how much performance/availability impact you allow on the primary database, you can have your standby site not lagging as single transaction from your primary. This is called "no data divergence/no data loss".
And yes, Data Guard is trully a disaster recovery solution. In fact, appart for database replication it is *the only true disaster recovery* solution I can think of. RAC for example is certanly not.
RAC is ofcourse does not has actual Data Gaurd feature . but if the the binaries or actual system fails then it switches the database to other node in a min time . and duplicating a databse even with RMAN does not use online redologs .
so i guess for ideal disaster recovery plan. it should be RAC with datagaurd.
RAC is high availability
Data Guard is Disaster Recovery
What does disater mean? When the building where the server is located is flooded then Data guard come into play. With RAC there is no way, if the building is burned then no matter how many servers you have the building is useless.
above disaster plan still holds good for this situation too. both the nodes can be placed in different cities and datagaurd can be set in 3rd city i assume floods will come to one city before extending to the other city .
I knew you would say that :D
FYI nodes between RAC must be a high gigabit speed interconnect, if you use that across cities your RAC is useless. I.E They must be next to each other in same place