8.3 Multisite Terminology
This section uses the following terminology:
Distributed vCloud – The generic concept of spreading vCloud resources and components across different locations.
Location – A physical location, a building,
or an entire physical datacenter with LAN connectivity, where vCloud
components are deployed. Single Site vCloud – A vCloud
that spans one or more locations that are connected with MAN connectivity. Multisite vCloud – A vCloud
that spans one or more locations that are connected with WAN connectivity. Figure 46. Distributed Deployment Options
Historically, a vCloud Director deployment was supported only in a single site or in a single location. However, this statement led to some confusion because it is not very deterministic. In fact, it is not unusual to find connectivity between different locations at large corporations that is better than the connectivity in a single site at smaller organizations.
For this reason this statement is clarified with a more deterministic approach and a single site is considered to be any local or distributed IT deployment where connectivity between any of the deployed components has a latency round trip time (RTT) of 20 milliseconds (or less).
This does not call out bandwidth requirements. This is because bandwidth is more of a problem from the perspective of an end-user experience than it is from a functional perspective. We assume that bandwidth in a MAN scenario is sufficient to not cause connectivity problems. However, we realize that, depending on the usage patterns of the vCloud, a relatively low bandwidth can result in higher response time for the user. The vCloud architect is responsible for planning according to the expected result and projected usage patterns.
These network characteristics are referred to as MAN connectivity. A single-site deployment is where one or more locations are used to host all of the vCloud Director components, and the RTT connectivity within a location or across two or more locations is less than 20ms.
If the vCloud Director
deployment has all of the components that fall within these connectivity characteristics, it is considered to be a single site and the deployment is fully supported.
If the distributed vCloud Director
deployment has components that fall outside of these
network characteristics, then it is a multisite implementation.
