Re: ORACLE RAC and ORACLE Standby


MTNorman wrote:
> Gabriel,
>
> In general terms, standby is better for disaster recovery and RAC is
> more useful for high-availability and load balancing. Both
> configuration provide an ability to write a cold database server backup
> with taking any downtime on your primary database instance.
>
> The standby database provides a local or off-site recovery instance.
> All database activity (DDL, DML) takes place on the primary instance.
> Archived redo logs are transmitted from the primary instance to the
> standby instance and applied to the standby instance to replicate the
> primary database updates. Although the connection between the two
> instances should be fast enough to support timely transmission of the
> log files, the functionality of the primary instance is not affected by
> a slow connection to the standby. A time delay on the redo log
> application to the standby database can provide a good "opps" cover
> for the primary (similar capabilities are also provided by flashback
> and logminer, depending on your oracle version). If the standby
> instance is not open for querying, no additional licensing is required
> - the primary instance licensing covers both since only one database
> will be open and in use at any time.
>
> RAC is two instances running on two (or more) different machines with
> shared or independent storage. Both instances must be licensed because
> queries and updates are running in both instances. A high-speed
> communication connection is required between the two instances because
> the instances are talking to each other constantly. When one database
> instance goes down, the "database" stills runs from the other
> instance. In 10g a read query can be picked up by the other instance
> without interruption. For updates, the connection can fail over to the
> second instance, but the transaction must be restarted (your custom
> code can detect this error and resubmit the update transaction).
>
> Load balancing capabilities of RAC (beyond normal even loading) include
> dedication of one instance for batch processing or one or two instances
> to serve one particular application. If one database (datastore or
> data warehouse) has a heavy overnight load and a smaller business hour
> load while another database (transaction processing) has a heavy
> business hour load and is mostly idle overnight, then you may be able
> to better utilize your processing power (and licensing costs) by
> creating an instance of each database on each server in a RAC.
> Overnight your data warehouse database has the cpu capacity of both
> servers. Suppose you have purchase enough cpu to run the data
> warehouse load jobs overnight (i.e. 4 procs) and then watch that sit
> mostly idle during business hours, while you also purchase capacity for
> peak business hours loads on your transaction processing database (i.e.
> 4 procs) that still mostly idle overnight. Instead of 8 procs (4 on
> each independent server) a RAC setup with 6 proc (3 proc on each
> server), may provide better cycle times at a reduced cost.
>
> Hope this helps,
> Margaret


Your licensing information about data guard is not true. In data guard,
you will have to pay for two licenses (if primary and standby are on
different servers - which is the case in OP's post).

As discussed RAC is a high-availability environment. RAC will work
only in a LAN environment, while data guard can be used in LAN as well
as WAN. If there is requirement for remote geographic failover, RAC is
out of the picture,

.

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