Failover Cluster Instance Share

  • Mike Scalise

    SSCrazy Eights

    Points: 8129

    Hi,

    I am using AlwaysOn Availability Groups in SQL Server 2016 with a primary and secondary replica. I have a Quorum file share witness on a separate file server. This file server needs to be rebooted, so I'm wondering what I need to consider before rebooting this box...

    Anyone have experience with this?

    Also, I have some flexibility here in terms of down time and making adjustments to the primary and/or secondary. I'm really looking for the best way to take down this server and get the AG to be back and synchronized as easily as possible--even if it means an outage or temporarily removing a database from an AG and adding it back in later, etc.

    Any guidance is appreciated!

    Thanks,

    Mike

    EDIT: I have since found this thread, which essentially answers my question.

    https://social.technet.microsoft.com/Forums/en-US/6ff3483c-af3a-41ff-a01f-69eaa1613e10/what-happens-to-cluster-2016-when-file-share-witness-goes-offline?forum=winserverClustering

    But would someone mind confirming that my assumption is right in that I wouldn't need to do anything special whatsoever to reboot the file share witness? Simply reboot it, let the AG continue to operate as normal, and then when the file share witness comes back online, carry on?

    Thanks,

    Mike

    • This topic was modified 1 month, 1 week ago by  Mike Scalise.

    Mike Scalise, PMP
    https://www.michaelscalise.com

  • Jeffrey Williams

    SSC Guru

    Points: 88603

    As long as your cluster maintains quorum - the AG will continue to function and you won't have any issues, that is why you have the file share witness.

    For a cluster to be healthy - you need to have enough quorum votes to count as more than 50% of the total quorum votes.  In a 2 node cluster - you have to configure the quorum to be at least 3 quorum votes.  If you only had 2 quorum votes - one for each node in the cluster then the count would be 1 out of 2 when one of the nodes was down - and 1 of 2 votes is not greater than 50% of total votes.

    So - you add the file share witness to get a total of 3 quorum votes and now you can maintain quorum as long as you have 2 of the expected 3 quorum votes up and available.  One node and the file share witness = 2 out of 3 votes...2 nodes and no file share witness = 2 out of 3 votes.  1 node and no file share witness = 1 out of 3 votes and cluster is not healthy and will be shut down.

    This is why we can restart any node in a cluster without taking the cluster down - as long as you maintain quorum the cluster is healthy and services will be up and available.

     

    Jeffrey Williams
    Problems are opportunities brilliantly disguised as insurmountable obstacles.

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  • Mike Scalise

    SSCrazy Eights

    Points: 8129

    Jeffrey Williams wrote:

    As long as your cluster maintains quorum - the AG will continue to function and you won't have any issues, that is why you have the file share witness.

    For a cluster to be healthy - you need to have enough quorum votes to count as more than 50% of the total quorum votes.  In a 2 node cluster - you have to configure the quorum to be at least 3 quorum votes.  If you only had 2 quorum votes - one for each node in the cluster then the count would be 1 out of 2 when one of the nodes was down - and 1 of 2 votes is not greater than 50% of total votes.

    So - you add the file share witness to get a total of 3 quorum votes and now you can maintain quorum as long as you have 2 of the expected 3 quorum votes up and available.  One node and the file share witness = 2 out of 3 votes...2 nodes and no file share witness = 2 out of 3 votes.  1 node and no file share witness = 1 out of 3 votes and cluster is not healthy and will be shut down.

    This is why we can restart any node in a cluster without taking the cluster down - as long as you maintain quorum the cluster is healthy and services will be up and available.

    Jeffrey,

    That's what I thought. Thank you for that information!

    Mike

    Mike Scalise, PMP
    https://www.michaelscalise.com

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