5.5

The placement engine uses the following criteria to select candidate datastores for a vApp and its virtual
machines.
n
Storage capacity
n
Storage policy
The placement engine filters out disabled datastores from the candidate list so that no virtual machine is
created on a disabled datastore.
The placement engine uses the network name to select candidate network pools for a vApp and its virtual
machines.
After the placement engine selects a set of candidate resources, it ranks the resources and picks the best
location for each virtual machine based on the CPU, virtual RAM, and storage configuration of each virtual
machine.
While ranking resources, the placement engine examines the current and estimated future resource use.
Estimated future use is calculated based on powered-off virtual machines currently placed on a given
resource pool and their expected use after they are powered on. For CPU and memory, the placement
engine looks at the current unreserved capacity, the maximum use, and the estimated future unreserved
capacity. For storage, it looks at the aggregated provisioned capacity provided by the cluster that each
resource pool belongs to. The placement engine then considers the weighted metrics of the current and
future suitability of each resource pool.
The placement engine favors resource pools that provide the minimum of unreserved capacity for CPU and
memory and free capacity for storage. It also gives lower preference to yellow clusters so that yellow
clusters are only selected if no healthy cluster is available that satisfies the placement criteria.
When a virtual machine is powered on, either as part of starting a vApp or on its own, the placement engine
runs to validate that the resource pool the virtual machine is assigned to has sufficient resources to support
the requirements of the virtual machine. This step is necessary because the resource availability on the
resource pool might have changed since the virtual machine was created on the resource pool. If the
resource pool lacks sufficient capacity to power on the virtual machine, the placement engine finds another
compatible resource pool on the provider virtual datacenter that satisfies the requirements of the virtual
machine and places the virtual machine there. This substitution might result in the migration of the virtual
machine's VMDKs to a different datastore if no suitable resource pools are connected to the datastore the
VMDKs are located on.
During concurrent deployment situations when a resource pool is close to capacity, the validation of that
resource pool might succeed even though the resource pool lacks the resources to support the virtual
machine. In these cases, the virtual machine cannot power on. If a virtual machine fails to power on in this
situation, start the power on operation again to prompt the placement engine to migrate the virtual machine
to a different resource pool.
When the cluster that a resource pool belongs to is close to capacity, a virtual machine on that resource pool
might still be able to power on even when no individual host has the capacity to power on the virtual
machine. This happens as a result of capacity fragmentation at the cluster level. In such cases, a system
administrator should migrate a few virtual machines out of the cluster so that the cluster maintains
sufficient capacity.
Download a vApp as an OVF Package
You can download a vApp as an OVF package.
Prerequisites
Verify that the vApp is powered off and undeployed.
Procedure
1 Click My Cloud.
vCloud Director User's Guide
66 VMware, Inc.