5.1

Select an Allocation Model
The allocation model determines how and when the provider vDC compute and memory resources that you
allocate are committed to the organization vDC.
Procedure
1 Select an allocation model.
Option Description
Allocation Pool
Only a percentage of the resources you allocate from the provider vDC are
committed to the organization vDC. You can specify the percentage for both
CPU and memory. This percentage is known as the percentage guarantee
factor, and it allows you to overcommit resources.
Starting with vCloud Director 5.1, Allocation Pool organization vDCs are
elastic by default. This means that the organization vDC spans and utilizes
all resource pools associated with its provider vDC. As a result, vCPU
frequency is now a mandatory parameter for an Allocation Pool.
Set the vCPU frequency and percentage guarantee factor in such a way that
a sufficient number of virtual machines can be deployed on the organization
vDC without CPU being a bottleneck factor.
When a virtual machine is created, the placement engine places it on a
provider vDC resource pool that best fits the requirements of the virtual
machine. A sub-resource pool is created for this organization vDC under the
provider vDC resource pool, and the virtual machine is placed under that
sub-resource pool.
When the virtual machine powers on, the placement engine checks the
provider vDC resource pool to ensure it still has the capacity to power on the
virtual machine. If not, the placement engine moves the virtual machine to
a provider vDC resource pool with sufficient resources to run the virtual
machine. A sub-resource pool for the organization vDC is created if one does
not already exist.
The sub-resource pool is configured with sufficient resources to run the new
virtual machine. The sub-resource pool's memory limit is increased by the
virtual machine's configured memory size, and its memory reservation is
increased by the virtual machine's configured memory size times the
percentage guarantee factor for the organization vDC. The sub-resource
pool's CPU limit is increased by the number of vCPU the virtual machine is
configured with times the vCPU frequency specified at the organization vDC
level, and the CPU reservation is increased by the number of vCPU
configured for the virtual machine times the vCPU specified at the
organization vDC level times the percentage guarantee factor for CPU set at
the organization vDC level. The virtual machine is reconfigured to set its
memory and CPU reservation to zero and placed.
The benefits of the Allocation Pool model are that a virtual machine can take
advantage of the resources of an idle virtual machine on the same sub-
resource pool and that this model can take advantage of new resources added
to the provider vDC.
In rare cases, a virtual machine is switched from the resource pool it was
assigned at creation to a different resource pool at power on because of a lack
of resources on the original resource pool. This might involve a minor cost
to move the virtual machine disk files to a new resource pool.
Pay-As-You-Go
Resources are only committed when users create vApps in the organization
vDC. You can specify a percentage of resources to guarantee, which allows
you to overcommit resources. You can make a Pay-As-You-Go organization
vDC elastic by adding multiple resource pools to its provider vDC.
Resources committed to the organization are applied at the virtual machine
level.
vCloud Director Administrator's Guide
54 VMware, Inc.