From an architecture standpoint, deployment modes can be of two types—simple and distributed.
As the name suggests, a simple installation deploys a single instance of each virtual appliance and installs all IaaS components, including the SQL database, in a single virtual machine. It is highly suited for development or proof-of-concept environments. Importantly, this deployment lacks high availability.
A distributed installation allows the separation of components that are best suited to the organization's needs and ideally used in production environments, and provides options for high availability. We have three distinct deployment modes: small, medium, and large. To learn more about these deployment modes, refer to http://www.vmware.com/files/pdf/products/vCloud/VMware-vCloud-Automation-Center-61-Reference-Architecture.pdf.