Oracle Database with Oracle RAC Architecture

< Hypothesis >

Assuming that we are running a single-instance database. And our database database must be up and running 24/7. If we fail to keep the database available for our users 24/7, we just have to go on vacation for ever. There will be no coming back. 

What if the server machine get damaged on its disk? What if a big earthquake and Tsunami hit our town so our office including the database server all go under the water? If the DB server fails, basically our database is down. And we have to start looking for a new job. My wife is going to be really really upset and sad, which is more scary than any other thing.

I would suggest to my DBA team that we should consider implementing Oracle RAC to our database because RAC could increase the availability and scalability of our database.

(1) Single-instance database 

One-to-one relationship between the database and the instance. So either the instance has a problem or the database storage has a problem, the database could become unavailable.

(2) RAC (Real Application Clusters)

One-to-many relationship between the database and the associated instances. An Oracle RAC database can have up to 100 instance, all of which access ONE database. A cluster comprises multiple interconnected computers or servers that APPEAR AS IF they are one server to the database users or applications. Oracle provides something, called "Oracle Clusterware" that can manage all this integration system.

    As shown in the picture below, each instance usually runs on a separate server(node). We could place each server in different locations(an extended distance cluster). This way, we could have our database still available for the user even if one server is down. For example(using the picture below), even if node 1 is down, we still have the other two nodes that can handle the data requests from the users. The RAC architecture could increase the availability of our database. 

    In addition, we can usually combine smaller commodity servers into one cluster. If we get more database users and need to increase our system capacity, we can simply add one or more commodity servers to the cluster (higher scalability)

Excerpted from http://download.oracle.com/docs/cd/B28359_01/rac.111/b28254/admcon.htm#i1058057

** In addition, Oracle Clusterware also enables to create a clustered pool of storage to be used by any combination of single-instance and Oracle RAC database. 

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< References >

http://en.wikipedia.org/wiki/Oracle_RAC

http://download.oracle.com/docs/cd/B28359_01/rac.111/b28254/admcon.htm