Hyper-V 2012 VM Placement by SCVMM 2012 SP1

Question

Hi,
I'd like to understand the logic behind VM placement in SCVMM 2012 SP1 and a 8 Node Hyper-v 2012 cluster. Each Node has 32GB RAM and each is a completely identical HP DL360.
Here is the current placement as performed by SCVMM
Node 1: 1 VM
Node 2: 2 VM's
Node 3: 6 VM's
Node 4: 1 VM
Node 5: 2 VM's
Node 6: 7 VM's
Node 7: 1 VM
Node 8: 1 VM
There are 2 x 16GB VM's, the rest of between 2GB and 8GB. Each of the overloaded hosts has a 16GB VM running on it.
I have a cluster reserve set to 1 Node failure. Why has it decided to favour Node 3 and 6? I appreciate the Maths to work out Node suitability are very complex but this seems rather odd.
Thanks in advance.
Eddie

Answer 1

Hi,
Please check “Preferred Owners” settings for each clustered resource.
There are some scenarios to help you understand failover process:
Scenario 1: If a node or resource fails and the Preferred Owner List has been defined, the Cluster Service fails the Group to the next available node in the Node List. The Node List is composed of the Preferred Owners List followed by the remaining nodes
arranged by their Node ID. The Node ID is defined when a node is joined to a cluster or if a node is evicted or and re-added.
Scenario 2A: If a resource fails and the Preferred Owner List is not set, the Group follows a Node List much like it did in Scenario 1. The Node List is built only from the Node ID. Upon a node or resource failure, resources follow a downward path failing
to the subsequent node in the Node List. When it reaches the last listed node in the Node List, it starts with the first node in the Node List.
Scenario 2B: If a node fails and the Preferred Owner List is not set for a group on that node, then an available node will be selected randomly for the group to be moved to. This will distribute the groups among the available nodes.
Scenario 3: If a Cluster administrator manually chooses Move group and selects Best Possible and the Preferred Owner List is configured, the Group will always start at the top of the Node List. As in Scenario 1, the Node List is composed of the Preferred
Owner List and the installation order.
Scenario 4: If, as Cluster administrator, you manually choose Move group and you select Best Possible and the Preferred Owner List is not configured, an active node is chosen randomly to host the group. Without the Preferred Owner List configured, it is
possible that a Group may move to a Node that is already running several other Groups.
We recommend that you configure the Preferred Owner list on a large node cluster if the load between nodes is significantly different or if the nodes are not homogeneous.
For more information please refer to following MS articles:
Failover behavior on clusters of three or more nodes
http://support.microsoft.com/kb/299631
Preferred Owners in a Cluster
http://blogs.msdn.com/b/clustering/archive/2008/10/14/9000092.aspx
Lawrence
TechNet Community Support