VCAP-DCD | Objective 2.1 | Map business Requirements to the Logical Design

Explain the common components of logical design

We’ve already briefly touched on the logical design back in Objective 1.1. The logical design is a lower level design than the conceptual, yet still should not focus on physical detail such as host names, IP addresses, LUN sizes etc. The logical design will should consider the conceptual design along with any constraints, risks and assumptions. This enables you to understand if the design will meet the goals and requirements whilst taking into account all of the constraints.

To summarise, the logical design is based upon the documented information in the conceptual design. It will consider all the constraints and risks associated with the project, whilst communicating all risks with recommended actions aligned to enable the project to progress without delay.

List the detailed steps that go into the makeup of a common logical design

  1. Consider the conceptual design, ensure constraints risks and assumptions are documented
  2. Document recommended items to workaround risks
  3. Do NOT include physical details such as hardware, vendors, IP’s, port numbers etc
  4. Ensure capacity analysis is kept in mind, however don’t be tempted to delve into physical detail
  5. Ensure all relationships are covered between all components of the infrastructure
  6. Diagram how the infrastructure components will be arranged
  7. Document with diagrams, tables and text
  8. Ensure all requirements are met!

Differentiate functional and non functional requirements for the design

A functional requirement specifies what a system should do. A requirement specifies a function that a system or component must be able to perform. A function is described as a set of inputs, the behaviour and outputs that should be measurable. A functional requirement for a vSphere design could be “The platform must support creation of new workloads from a template” or “The platform should allow for 20% growth over the next 3 years”.

A non-functional requirement specifies how the system should be have. A non-functional requirement is a statement of how a system must behave, it is a constraint upon the system behaviour. A non-functional requirements specifies criteria that can be used to judge the operation of the system rather than specific behaviours. Non-Functional requirements can also be constraints. A non-functional requirement for a vSphere design could be “The platform will be built on VCE’s Vblock infrastructure” or “vSphere 5.1 will be used over vSphere 5.5 to ensure application support”.