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I have 3 servers 1 production 1 standby and 1 just sitting there.

I want 1 to stay production and I have been working on setting up an MSSQL automatic failover cluster between the production server and the standby server. I require a witness server and an active directory.

My question is: Can I install the MSSQL witness server on a Domain Controller? If not, WHY?

This would allow me to NOT virtualize or purchase a fourth machine. Has anyone done this in a production environment?

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What do you mean by a MSSQL 'monitor server'?

A typical MSSQL MSCS cluster requires a domain controller and (usually) two nodes which can both run the MSSQL service (and a whole bunch of shared storage). The nodes between them watch each other for availability and have the capability of taking ownership of a service if the node running that service fails. This is a fairly standard configuration that's used in loads of places.

If you're trying to do HA MSSQL without using MSCS, I'd probably suggest it's a bad idea.

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My apologies. The Witness server. Required to create the Quorum. – Campo Apr 6 '11 at 18:28
Ah, ok, I see. I've never used a witness server as I've always one with a shared disk quorum. I don't see any reason why you couldnt have it on the DC, but the question will always be "what if the witness server goes down?" and "What if the DC goes down". If you test it and find you can keep MSSQL running if you yank the power on your DC/witness, it might stand up in the future. – growse Apr 6 '11 at 21:53
No worries always appreciative of the help. Can you mark me up to get some attention then :) The whole point is a quorum if any of the three go down I will get notice and be able to act. The monitor is there to facilitate the automatic failover so we can maintain uptime while I deal with the issues. Basically there if the primary member goes down it will activate the other member server automatically. – Campo Apr 6 '11 at 21:54

This isn't clustering you are referring to, it is mirroring. Yes, you can setup the DC as a witness server, but it's not recommended.

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