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Wilfred van Dijk avatar image
Wilfred van Dijk asked

2node AlwaysOn AG:where to put the witness

I have a 2 node AOAG cluster (MSSQL2014), replicas are on a different subnet on different locations. There's no 3rd location. OS is Windows Server 2012R2. I was wondering: what is the best location for the fileshare witness. On the primary or on the secondary? How will dynamic quorum behave?
clusteralwayson
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FSW never goes within the cluster it is used on, should go on a separate cluster or another server altogether. Also, what mode is your AG going to be in if your only secondary is at a different location (assuming you mean it will sync over a WAN link)? What happens when that WAN link slows to a crawl and your AG gets out of sync?
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Kev Riley avatar image
Kev Riley answered
If there is no third location why bother with a witness at all. Assign voting so that the 'primary' has a vote, and the secondary doesn't. If the network link goes, cluster stays on the 'primary' and the AG stays up. If you keep voting such that each node has a vote, and the links go, then you are at the mercy of dynamic voting, and whichever node it chose to weight. In Windows Server 2012 R2 you can control this with the LowerQuorumPriorityNodeID property. You'll never have fully automatic failover here as there is no true independent witness.
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I didn't read beyond the question - Ockham would be ashamed of me. This, of course, is the correct answer for the problem described.
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KenJ avatar image
KenJ answered
If the two locations lose network connectivity, do you want the primary to stay online? If so, place the file share witness with the primary. [Failover Cluster Step-by-Step Guide: Configuring the Quorum in a Failover Cluster][1] on technet might be good further reading [1]: https://technet.microsoft.com/en-us/library/cc770620%28v=ws.10%29.aspx
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