VMware Cloud Director system administrators can create organization virtual data centers (VDC) by using the Flex allocation model. With the combination of Flex allocation and VM sizing policies, system administrators can control the CPU and RAM consumption at both the VDC and the individual virtual machine (VM) levels. The Flex allocation model supports all allocation configurations that are available in the existing allocation models.

You can convert all non-Flex organization VDCs into Flex VDCs by using the Service Provider Admin Portal, to publish an incompatible compute policy to the non-Flex organization VDC.

Note: By using the VMware Cloud Director API, you can convert the allocation model of any organization VDC.
When creating a Flex organization VDC, system administrators control the following parameters of the organization VDC:
Parameter Description
Elasticity Activate or deactivate the elastic pool feature.
Include VM Memory Overhead Include or exclude memory overhead in this VDC. When set to true, you might not be able to use the full capacity of the VDC because the memory overhead of every powered-on VM is also taken from the available capacity of the VDC. When set to false, the memory overhead is taken from the provider VDC and not from the allocated capacity of the VDC.
CPU allocation The amount of CPU allocated to this VDC in MHz or GHz. The CPU allocation defines the CPU capacity of the VDC. The total CPU used by all VMs running in the VDC cannot exceed this value.
CPU limit

The CPU limit defines the CPU quota of a VDC. In most cases, the CPU limit is equal to the allocated CPU capacity of the VDC.

Sometimes, you might be required not to allocate any CPU to the VDC, as in the pay-as-you-go model. In this case, you must set a quota on the overall CPU consumption by setting the CPU allocation to zero and the CPU limit to a non-zero value.

You might also use this setting to allow an unlimited CPU quota. If set to unlimited, the backing resource pools of the VDC in vCenter Server get unlimited CPU.

CPU resources guaranteed The percentage of CPU allocation that is physically reserved for the VDC.
vCPU speed The default vCPU speed for VMs in the VDC.
Memory allocation The amount of memory allocated to this VDC in MB or GB. This parameter defines the total memory capacity of the VDC. The total configured memory by all VMs running in the VDC cannot exceed this value.
Memory limit

The maximum amount of memory for this VDC in MB or GB. In most cases, the memory limit is the same as the memory allocation. In a non-elastic VDC, VMware Cloud Director uses this amount as a memory limit on the resource pool backing this VDC in vCenter Server. For elastic VDCs, VMware Cloud Director distributes this amount to all resource pools and applies it as a resource pool memory limit.

The memory limit must be higher than the memory allocation when you create a VDC with 100 percent memory reservation and the Include VM Memory Overhead setting is false. In this case, if the memory limit is the same as the memory allocation, some VMs might not power on because vCenter Server does not allow the total memory requirement of the resource pool to expand beyond the value set in the memory limit.

Memory resources guaranteed The percentage of memory allocation that is physically reserved for the VDC.
Maximum number of VMs The maximum number of VMs in the VDC.

As a VMware Cloud Director system administrator, you can configure a Flex organization VDC to be elastic or non-elastic. When Flex organization VDCs have the elastic pool feature enabled, the organization VDC spans and uses all resource pools that are associated with its provider VDC. In VMware Cloud Director 9.7, if you convert a non-elastic organization VDC to an elastic organization VDC, you cannot convert the same organization VDC back to a non-elastic.

The Flex allocation model supports the capabilities of VM sizing policies without any constraints that other allocation models have. In the Flex allocation model, the VM compute resource allocation depends on the VM sizing policies. If you do not define a VM sizing policy for an organization VDC, the compute resource allocation depends on the organization VDC allocation model. Using the combination of the Flex allocation model and the organization VM sizing policies, a single organization VDC can accommodate VMs that use configuration that is common for all other allocation models. For more information, see Understanding VM Sizing, VM Placement, and vGPU Policies.

To create a Flex organization VDC, you can use the VMware Cloud Director Service Provider Admin Portal or the VMware Cloud Director API. For information about VMware Cloud Director API, see the VMware Cloud Director API Programming Guide.