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.

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Windows Server Clustering
Windows Server Clustering
Windows Server: A family of Microsoft server operating systems that support enterprise-level management, data storage, applications, and communications.Clustering: The grouping of multiple servers in a way that allows them to appear to be a single unit to client computers on a network. Clustering is a means of increasing network capacity, providing live backup in case one of the servers fails, and improving data security.
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  1. AniyaTang-MSFT 12,421 Reputation points Microsoft Vendor
    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 106.5K Reputation points
    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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  2. Alex Bykovskyi 1,846 Reputation points
    2023-05-15T14:55:30.8733333+00:00

    Hello,

    As gentlemen already mentioned, cluster will be still working in case there is no connection to cloud witness. Two nodes will be the majority. Check for more information:

    https://techcommunity.microsoft.com/t5/failover-clustering/understanding-quorum-in-a-failover-cluster/ba-p/371678

    As an alternative to cloud witness, you can use StarWind VSAN, which will create replicated iSCSI device between your nodes and can be used as quorum witness disk.

    https://www.starwindsoftware.com/starwind-virtual-san

    Cheers,  
    Alex Bykovskyi  
    StarWind Software  
    Note: Posts are provided “AS IS” without warranty of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose.

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