Number of Mirroring witnesses allow


Within database mirroring are you allow more than one witness..?

I have the following setup:

Primary server in Datacentre1 and Failover server in Datacentre2.

Where is the best place to install the witness? We currently have a 3rd datacentre, would the witness be better in there or with the principle?

I am thinking of user SQL Express 2008 as the witness, is this advised?

Thanks in advance.

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asked Dec 11, 2009 at 08:36 AM in Default

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2 answers: sort voted first

Haven't implemented database mirroring, so this is just from what I've read....

One witness only seems to be the setup, as the purpose of the witness is to independently ensure that only one of the instances is serving the database, when the instances lose connection with each other. Not sure how thta would work if you had multiple witnesses, as then you would also need a witness-witness!

Obviously the witness needs to be on a physically different machine to either of the database mirror instances, and keeping it separated into another datacentre could improve your resilience.

SQL Express 2008 can be used as a witness, however Microsoft recommend

that every server instance that is used as a witness correspond to the minimum configuration that is required for the SQL Server Standard version that you are running

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answered Dec 11, 2009 at 09:01 AM

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Although I have never tried to set up more than one witness, I do not think there is any realist way to do it and I am not entirely clear why you would want to either. Even if you could, it seems like it would generate more problems than benefits.
Dec 11, 2009 at 05:32 PM TimothyAWiseman
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The placement of the Witness would come down to the integrity of your networks. You don't want false failovers.

That being said, I would probably locate it in the DR datacentre so that the Standby and it can form a quorum should the Primary fail and the third datacentre not be accessible for some reason.

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answered Dec 11, 2009 at 10:17 AM

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asked: Dec 11, 2009 at 08:36 AM

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Last Updated: Dec 11, 2009 at 09:10 AM