RAC and dataguard

With reference to this thread
is Dataguard and standby dbs is HA
RAC and DATAGAURD are two different approches for high availability and desaster recovery.
We are planning to implememt RAC and DATAGAURD but there are budget issues also.
With RAC As i understand we have multiple instances governing a single database. So multiple node/machines governing a single database server.
With DATAGAURD,we have a DR solution at another location.If the primary server fails,standby database takes up the role of primary.
With RAC alone,if any node fails, there is another node to do instance recovery or the server still continues. But what if database server crashes. WIth RAC alone and no dataguard, won't it allow downtime?

Hi Hashmi,
RAC and DataGuard are indeed different things, as you understood.
Regarding your question, there is no database server, that's the whole thing. There is one database (which resides on external redundant storage like Netapp, EMC, etc.) and there are several servers that are running the instances. Downtime will occur only if the storage crashes. And if you don't trust your storage you can have ASM redundancy, so storage failure will not cause downtime as well.
The down side, is that there is one database, so if you have logical corruption, human error, or something similar you can loose data or have downtime.
However, the high availability is real.
In DataGuard, once the primary is down it takes some time (not long) to activate the standby, but it has a different IP, so you should configure your DNS/clients (in advance or at failover) to connect to the activated standby.
HTH
Liron Amitzi
Senior DBA consultant
[www.dbsnaps.com]

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