Geek Seek on Mon, 18 Feb 2013 11:01:37

Hello All,

1-  How many nodes are actually required to make a two-2 node cluster work? do we require a third node for majority?

2-  Are there any limitations of clustering with respect to number of instances or database engines?

3-  If the nodes are vmware virtual machines, would the setup require any specific changes?

thanks in advance.



Uri Dimant on Mon, 18 Feb 2013 11:37:16

Two nodes

IIRW 25 instances per server on the cluster.

Geek Seek on Tue, 19 Feb 2013 13:32:43

Thanks for the reply.

1-  So, there is no need for any third node for maintaining quorum?  How would application know when to shift to server 2 in case server 1 fails? 

2-  I am about to do it on two virtual machines.  Are there any special configuration required with respect to that?  Such as both of them sharing the same storage?


davidbaxterbrowne on Tue, 19 Feb 2013 14:36:53

1) For quorum  you should have an odd number of nodes or add an additional quorum resource (eg a file share witness).

2) They only need to share storage if you want to install a Failover Cluster Instance (FCI).  If you plan to use AlwaysOn Availability Groups (AG), then no shared storage is required.  VMware has guidance and on configuring shared storage WSFCs.


Geek Seek on Tue, 19 Feb 2013 19:07:41

Thanks for the reply.

So, in other words in no configuration it is possible to setup a two-2 node cluster with only two machines.  There has to be a witness server as well.  In total, three machines would be required.  Correct me if i am wrong?

davidbaxterbrowne on Tue, 19 Feb 2013 20:33:41

No.  It is quite possible.  If you don't have a file server available to serve as a third quorum vote then you won't be able to have automatic failover between your nodes.  You can also use a shared disk as a quorum resource.

With only two machines and no file share or disk for a quorum resource, it is quite possible and supported to have a two-node cluster with no extra quorum.  The cluster will go offline when any voting node goes down or communication between them is lost.  This is not usually desirable behavior, thus the recommendation to add a third vote.