Note: This article is based on VMM 2008  and might not apply to VMM 2012 (R2)

One of the top questions that I keep hearing from our customers is to explain the ‘over-committed’ status and why we sometimes display this status. An example of when this status might be displayed is when attempting to migrate a VM to a particular host, depending on what is already on the destination the ‘over-committed’ status might be displayed.

HAVM Placement and “Over-committed” Status

When placing a highly available virtual machine, the placement process in VMM calculates whether adding a new virtual machine to a host cluster will over-commit the cluster based on the cluster reserve configured for the host cluster in VMM. The cluster reserve specifies the number of node failures a cluster must be able to sustain while still supporting all virtual machines that are currently deployed on the clustered hosts. If a host cluster cannot withstand the specified number of node failures and still keep all of the virtual machines running, the cluster is placed in an Over-committed state, and the hosts are not available for placement. An administrator can override this and place an HAVM on a host in an over-committed cluster during manual placement. Cluster reserves are a unique feature of VMM.

For example, if you specify a node failure reserve of 2 for an 8-node cluster, the rule is applied in the following ways:

· If all 8 nodes of the cluster are functioning, the host cluster is marked Overcommitted if any combination of 6 nodes (8-2) in the cluster lacks the capacity to accommodate existing virtual machines.

· If only 5 nodes in the cluster are functioning, the cluster is marked Overcommitted if any combination of 3 (5-2) nodes in the cluster lacks the capacity to accommodate existing virtual machines.

VMM’s cluster refresher updates the host cluster’s Over-committed status after each of the following events:

· A change in the cluster reserve value

· The failure or removal of nodes from the host cluster

· The addition of nodes to the host cluster

· The discovery of new virtual machines on nodes in the host cluster

The cluster reserve is set on the General tab of the host cluster properties. For a procedure, see How to View and Modify the Properties of a Host Cluster (http://go.microsoft.com/fwlink/?LinkID=162986).

The above information is available in the System Center Virtual Machine Manager 2008 R2 Operations Guide.

Download Virtual Machine Manager Documentation

http://technet.microsoft.com/en-us/library/ee441285.aspx

Note: This information was originally provided by Mike Briggs, Senior Support Escalation Engineer, on the System Center Virtual Machine Manager Team blog:

http://blogs.technet.com/scvmm/archive/2009/12/07/what-does-over-committed-status-really-mean.aspx