Because this allocation model assigns all setting on a resource pool basis, updates to this model do not require a shutdown and restart of the virtual machines to pick up the changes. Based on the settings chosen, this model could be considered as one of the best models because the consumer has control over how the pool of resources is divided among the virtual machines.

The provider must monitor the use of the Maximum number of VMs setting. If this is left as unlimited and the consumer does not set any per virtual machine reservations, there is potential for overcommitment. A consumer can, in theory, deploy more or larger virtual machines than the pool is configured for (additional resources such as memory could be paged out to satisfy the configuration). Assigning a limit to the maximum total virtual machines can help control this and keep the pool within the size it should be.

Huge virtual machines can be created using this model, but it is important to understand the role that overhead reservations play along with the standard per virtual machine reservations. Understanding the effect of these settings on vSphere is crucial for implementation.

See the following external reference for more information: VMware vSphere 5.1 Clustering Deepdive (Chapter 13). Available from Amazon.com.