An allocation model determines how and when the allocated provider virtual data center (VDC) compute and memory resources are committed to the organization VDC in VMware Cloud Director.

The following table shows the vSphere resource distribution settings at the virtual machine (VM) or resource pool level based on the organization VDC allocation model.
Flex Allocation Model Elastic Allocation Pool Model Non-Elastic Allocation Pool Model Pay-As-You-Go Model Reservation Pool Model
Elastic Based on the organization VDC configuration. Yes No Yes No
vCPU Speed If a VM CPU limit is not defined in a VM sizing policy, vCPU speed might impact the VM CPU limit within the VDC. Impacts the number of running vCPUs in the Organization VDC. Not Applicable Impacts VM CPU Limit Not Applicable
Resource Pool CPU Limit Organization VDC CPU limit apportioned based on the number of VMs in the resource pool. Organization VDC CPU allocation Organization VDC CPU allocation Unlimited Organization VDC CPU allocation
Resource Pool CPU Reservation Organization VDC CPU reservation is apportioned based on the number of vCPUs in the resource pool. Organization VDC CPU reservation equals the organization VDC CPU allocation times the CPU guarantee. Sum of powered on VMs and equals the CPU guarantee times the vCPU speed, times the number of vCPUs. Organization VDC CPU allocation times the CPU guarantee None, expandable Organization VDC CPU allocation
Resource Pool Memory Limit Organization VDC memory limit is apportioned based on the number of VMs in the resource pool. Unlimited Organization VDC RAM allocation Unlimited Organization VDC RAM allocation
Resource Pool Memory Reservation Organization VDC RAM reservation is apportioned based on the number of VMs in the resource pool. The organization VDC RAM reservation equals the organization VDC RAM allocation times the RAM guarantee. Sum of RAM guarantee times vRAM of all powered-on VMs in the resource pool. The resource pool RAM reservation is expandable. Organization VDC RAM allocation times the RAM guarantee None, expandable Organization VDC RAM allocation
VM CPU Limit Based on the VM sizing policy of the VM. Unlimited Unlimited vCPU speed times the number of vCPUs Custom
VM CPU Reservation Based on the VM sizing policy of the VM. 0 0 Equals the CPU speed times the vCPU speed, times the number of vCPUs. Custom
VM RAM Limit Based on the VM sizing policy of the VM. Unlimited Unlimited vRAM Custom
VM RAM Reservation Based on the VM sizing policy of the VM. 0 Equals vRAM times RAM guarantee plus RAM overhead. Equals vRAM times RAM guarantee plus RAM overhead. Custom
The non-flex VDC allocation models are legacy models. The legacy models are:
  • Reservation Pool Model
  • Allocation Pool Models
  • Pay-As-You-Go Model

Converting a Legacy VDC Allocation Model to a Flex Allocation Model

The Flex Allocation Model provides full flexibility to control CPU and memory consumption at the VDC and individual VM levels, supports all allocation configurations, and can replace the legacy models. Unlike legacy models, the Flex Allocation Model is compatible with all values of a VDC compute policy.

You can add a VM placement and a VM sizing policy to a VDC with an elastic allocation pool model, non-elastic allocation pool model, pay-as-you-go model, or reservation pool model. Using the VMware Cloud Director GUI, if you add a VM placement or VM sizing policy to a VDC and the policy is not compatible with the existing VDC allocation model, a dialog box appears with a notification and the option to convert the VDC to a flex organization VDC. You can also use the VMware Cloud Director API by running a PUT request on the organization VDC and change the VDC AllocationModel to Flex.

VM Policy Compliance

Legacy VDC conversion does not cause VM non-compliance. If an administrator changes the VM compute values or VM group membership of a VM directly in the vCenter instance, a VM can become non-compliant with the assigned VM sizing or VM placement policy. A VM can also become non-compliant if a user with the necessary privileges changes the VM reservation and limit values by using the VMware Cloud Director API. If there is a non-compliant VM, VMware Cloud Director Tenant Portal UI displays a warning message. The tenant can see detailed information about the cause for the non-compliance and can make the VM compliant again, which reapplies the policies to the VM.