In Failover Cluster Manager, if you go through the quorum configuration wizard and try to use a DFS share, it will fail on the Summary Page with this dialog: We have added logic to check to check if the share is going to DFS.
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Microsoft does not support running a File Share Witness on DFS shares.įor Windows Server 2019, additional safeguards have been added to help protect from misconfigurations. Once the storage replication begins again, a very possible outcome is that everything that was written on one of the sides is now gone. However, remember, each side had the SQL databases being written to. When connectivity is restored between the sites and we get back to our normal cluster view again, we think everything is all roses again. So as far as each sides view of membership, they have quorum and SQL clients are connecting and writing/updating the databases. For those not so familiar with Failover Clustering and all its jargons, this is known as a split brain. Site B nodes see it has the witness, so it starts bringing everything online, which would include SQL and its databases. It goes to connect and DFS Referral sends it to one of the other machines and connects. Site B nodes do what it is supposed to which is to arbitrate to get the Cluster Group and the witness resource. Since it cannot communicate to Site A, it has no idea what is going on. Over on Site B, is where the problem occurs.
Because it is running SQL already, it stays status quo. Site A already has the file share witness and places a lock on it so no one else can come along and take it. What has happened is there is a loss of connectivity between the two sites. But this is what can happen if there is some sort of break in communications between the two sites. So, it would look something like this.Īll is fine, dandy and working smoothly. The cluster connects to a file share witness that is a part of DFS share. Each side has shared drives utilizing some sort of storage replication ( Storage Replica for those Ned fans ). Let's take the example of a 4-node multisite cluster with two nodes at each site running SQL FCI. Let me give you an example of what can happen on a Windows Server 2016 Cluster. I am specifically talking about putting a cluster File Share Witness on a DFS share. DFS is a great feature with numerous deployments out there. Please do not misunderstand that this is a stance against DFS. This is an awfully bad idea and one not supported by Microsoft. However, over the years, we have seen where this share is put on a DFS Share.
As a recap, the File Share Witness is designated a vote in the Cluster when needed and can act as a tie breaker in case there is ever a split between nodes (mainly seen in multi-site scenarios). One of the quorum models for Failover Clustering is the ability to use a file share as a witness resource.
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