Oracle RAC vs Dataguard

RAC Overview:

         

RAC means that two or more computers are sharing a common set of disk.  All of the computers have read write access to the data in the single (one) database. If one computer (node) fails in the cluster - work continues as before - the database never goes down

Good: RAC is a good solution for hardware failures, system failures, and software failures.

Good: Sharing resources across servers.

Good: RAC addresses system failures such as s node failures, or instance crashes.

Good: load balancing: you have multiple instances running on the same database and any new connection is routed to the instance with less work load in the available instances.

Disadvantage: RAC is very expensive – you need many servers, fiber channel infrastructure, eventually Storage Area Network. Of course this cost money.

Data Guard Overview:

Data guard is a configuration, which has at least one standby database of the primary database. The primary database can have one or more standby databases.

Good:  This enables recovery from site disasters (fire, flood, explosion, whatever) oracle data corruptions.

Good:  Can use the data guard site for read-only reporting purposes if we required.

Good:  Data Guard provides data protection.

Disadvantage:  The Data Guard option is only available in the enterprise edition of oracle software.

Few Difference between Oracle RAC and Data Guard:

•           RAC has one database and several instances associates with it, but data guard has several databases (one primary and others standby databases).

•       RAC is the recommended solution for instance, software and hardware level failures. Data guard is the recommended solution for the SITE failures.

•        RAC must have a shared storage, which can be accessed from all the nodes of the system, but in data guard there is no shared storage, which is common for all the sites.

•         RAC is Active-Active solution, expensive cost wise:: Data guard is Active-Passive , less expensive compare than RAC.

•      RAC nodes are placed within the same premises (physically close together): Data Guard site can be physically remote (different sites at unlimited distances from each other).

•       RAC licensing is more expensive than Data Guard licensing: Data Guard is not an extra cost option, but you need to pay for a full oracle license at the standby node.