What is the difference between possible owner and preferred owner in SQL Server Cluster?
Possible owners are defined at the resource level and dictate which nodes in the Windows cluster are able to service this resource
For instance, you have a 3 node cluster with Node A, Node B and Node C. You have a clustered disk resource “MyClusteredDisk”, if you remove Node C from the possible owners of the clustered disk resource “MyClusteredDisk” then this disk will never be failed over to Node C.
Preferred owners are defined at the resource group level and define the preferred node ownership within the Windows cluster
For instance, you have a 3 node cluster with Node A, Node B and Node C. You have a cluster resource group “MyClusteredGroup” which contains various disk, IP, network name and service resources. Nodes A, B and C are all possible owners but Node B is set as the preferred owner and is currently the active node.
The resource group fails over to Node C as Node B stops responding on the Public network due to a failed NIC. In the Resource group properties on the failback tab you have this set to immediate.
You fix the NIC issue on Node B and bring it back up on the network. The resource group currently active on Node C will without warning immediately attempt to failback to Node B. Not a good idea if this is a Production SQL Server instance, so use caution when configuring preferred owners and failback.