Redundant Server

Hi, I don't know if this is the right forum.... Could someone explain to me what is a Redundant Server is and how it differs with "other Servers"?

Thanks

SQL Server 2000 High Availability Series: Minimizing Downtime with Redundant Servers


From; What are redundant servers and how do I incorporate a redundant server license file for MATLAB and associated products? - 1-1924T

What is a redundant server?

If a large number of licenses are governed by a single license server, any failure of the server becomes a major event. To prevent problems, it may be desirable to set up redundant servers so that if one server goes down, the license manager can still function.

In the redundant server configuration, three machines are designated to be license servers. All three machines must be running at the time the license manager is started. However, once the license manager is running, only two machines need to be running at once; this is called a quorum. When a quorum exists the license manager can continue to run.



From; Loadbalanced and Redundant computing

Redundant servers
Creating a system using redundant servers is in itself much more complex than a system with a single server. Not only does it cost more time, but it also introduces more bugs than if you hadn't added this hairy code. On the other hand, bugs in this code is often within your reach to fix in a later stage.

The story for this kind of development may go like this:

As in the single server case, you'll get to maybe 95% reliability in the first year. The second year, you'll be adding the code for load balancing and redundancy and that will lower the reliability to maybe 90%. Not only did you introduce more code, you also did not spend time to make the basic server code better, so it's a double loss in this sense.

On the other hand, if you now install two servers, the 90% reliability turns into a 99% reliability, if no bugs are in the basic algorithms (which some are, of course).

Bugs in the balancing algorithms affect all servers alike, so the 99% number would go down. On the other hand, such bugs are generally easy to detect and correct during pilot phases, so after a short while we're back up close to the 99% figure.

Now, if you're not happy with the 99% number, simply add more servers. One more and you'll get 99.9%. This number is simply unachievable by any other method. I may exaggerate here, but not by much, actually.


http://www.kantech.com/WebApps/getDo...N1317-0410.pdf

I hope this helps with your query.

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Or more simply, a redundant server is a backup server, up and running on the network, that can take over instantly if the primary server fails.

Often, if the primary and secondary are both functional, both will share duties, increasing overall throughput. But in the event one fails, the redundant box takes over full duties until the primary is back on line.

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Thank you very much Digerati... Now I know.