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Say you set up a Windows Server Failover Cluster consisting of two nodes, on Windows Server 2008 R2 Enterprise.

Now when you want to configure quorum you can use either a remote shared folder, or a shared disk (unless your nodes are separated geographically).

I'd love to know more about when to use a disk witness and when to use a file share witness. What are the differences? Does it matter at all?

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Like you said; shared disk when nodes are connected to the same storage systems (which often isn't geographically seperated), file witness for everything else.

One good example of doing file share witness is when you want to avoid split-brain scenarios between two sites. You can set up a third site with only a single server and run a file server there for witness quorum. This way one of the sites will have a very likely chance to gain quorum through connectivity to the third site.

It all comes down on how long you can stay offline. Cluster elections with enough quorum votes can enable automatic failover. Just make sure you have an even number of nodes on both primary and secondary site before you start using quorum witness on a third site.

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Why is a disk witness preferred when the nodes are connected to the same storage system? It may be faster, but it doesn't really matter practically, does it? Isn't the traffic close to zero? Currently I set up a file share witness even though I could just as easily have set up a disk witness (the machines are running on the same ESXi host). Is there anything wrong with that? :) – arex1337 Oct 7 '12 at 0:43
Well, it depends. If you're using cluster services without shared disks then it would be more work than needed to implement disk based witness. If you are using shared disks, then you (usually) trust your storage to be more available than your network/file server. A single file server with witness share is a SPOF compared to a SAN with dual controllers and so on. – pauska Oct 7 '12 at 1:27

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