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What is called "Failover clustering"? (SQL server)

pepr
pepr asked
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Last Modified: 2010-04-21
The term is used in the sample test exam, but it is not described in the Self-paced Training Kit book...

Hi experts,

I am learning from the Microsoft SQL Server 2005 Implementation and Maintenance, self-training kit. I cannot find the explanation of the term there.

Thanks for your time and experience,
    Petr
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Failover clustering is also known as Active / Passive clustering.

You have one node in continual use and if it fails, the other node takes over the clustered resources. The passive node polls the active one, and if the failure threshold is reached, it moves the resources to its own control.

The alternate method is load balanced clustering where both nodes are in use and if one fails, the other carries on at lowered performance.
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In one of the questions the Failover clustering is the part of the correct answer. The other part is Database mirroring. Then, if I understand it well, Database mirroring (in High Availability mode) needs 3 instances of the SQL server (principal, mirror, and witness). This way, it can be viewed as built on the top of the basic behaviour of the SQL Server implementation (or uses the existing features of the server).

On the other hand Failover clustering must be implemented on lower levels of implementation of the SQL Server. The clustered server behaves as if it was a single instance; however, it is installed on more hardware pieces that act together.

Is asimple SQL Server is to a clustered SQL Server what is a simple hard disk to RAID 1. Is it a good parable?

To Kieran_Burns: Is it general terminology related to whatever implementation of an SQL server? If yes, is the Database Mirroring (in the terms of MS SQL 2005) the mentioned Active/Passive clustering (depending on whether witness server is used or not) a kind of clustering implemented on higher abstraction level than other kinds of implementation of clustering?

Thanks,
   Petr
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Thanks for clarification.

Petr
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