what happens if the cloud witness is unreacheble for a two node cluster

Angel Rendiles 20 Reputation points
2023-05-12T19:06:52.3466667+00:00

Hi, first of all thank for all your incoming aswers.

I'm trying to deploy a two node WSFC and then create a SQL Server Availability Group.

The scenario is that in a building, there are two Datacenter and I installed a server in each datacenter. So the problems is that I need implement a Quorum Witness because I have only two nodes, but I have just two fisical places that are the two datacenters, so if the datacenter who host the qourum and a node too, suffers a power outage, all cluster will go down.

So I'm considering use Cloud Witness with a Azure Storage Account, but internet connection in the local network could be unestable in certain moments, actually the network can lost internet connection for 1 o 2 days.

The real question is, If nodes lost connection with the cloud witness, all cluster goes down? It´ll be common that nodes still have local network connection between them, but if internet connection fail, they won't reach cloud witness.

Windows for business | Windows Server | Storage high availability | Clustering and high availability
SQL Server | Other
SQL Server | Other

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Anonymous
2023-05-15T06:20:47.93+00:00

Hi @Angel Rendiles

If the witness fails, you still have two votes (nodes one and two) that represent a two out-of-three majority. It doesn’t matter if you lose the witness whether it's disk, file share or cloud witness because you still have a two out of three votes. Because nodes one and two are still healthy, SQL will keep working on node one without any failure or failover.

For more details, you can refer to this link: https://continuitycentral.com/index.php/news/technology/2774-understanding-windows-server-cluster-quorum-options.

Best regards,

Aniya

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  1. Erland Sommarskog 138.5K Reputation points MVP Volunteer Moderator
    2023-05-14T20:47:19.07+00:00

    Clustering is not my expertise, but my understanding is that the cluster will jog along, since it still has quorum. That is, two of three are alive.

    But these two data centres, how far apart are they? And do you plan to use synchronous or asynchronous commit in your AG?

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  3. Nizamettin Özpolat 0 Reputation points
    2026-10-27T15:08:10.7533333+00:00

    If any of the nodes is lost after loosing witness, whole cluster goes down. Because both nodes have votes. This is weired to me. Dynamic quorum works differently in a 3 node cluster environment, and 2 nodes + witness environment.
    In a 3 node cluster, when any of the node is lost, dynamic quorum works and strips off one of the votes.
    In a 2 node + witness cluster, when witness is lost, both votes remains.
    Is this a design or a bug? Microsoft documentations explains only node losses, not witness loss. Is loosing a witness impossible?

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