During the discovery process, information is collected on the business and technical goals of the virtualization project. This information must be analyzed in order to determine the design factors.
The design factors that must be determined are as follows:
Requirements
Constraints
Assumptions
Risks
Determining the requirements, making and proving assumptions, determining constraints, and identifying risks form the conceptual design and provide the foundation to build on for the logical design. Business and technical design factors identified as part of the conceptual design will be mapped to the resources that are necessary to satisfy them during the logical design process. The conceptual design stage is the next phase in the design process as shown in the following diagram:
In our example design, after conducting interviews with stakeholders and performing technical assessments of the environment, the following information has been collected about the project's goals, current environment...
The design requirements specify the functions that the design must perform and the objectives that the design must meet.
There are two types of requirements: functional requirements and nonfunctional requirements. Functional requirements specify the objectives or functions that a design must meet. Nonfunctional requirements define how the design accomplishes the functional requirements.
Typical functional requirements include the following:
Business goals
Business rules
Legal, regulatory, and compliance requirements
Application system requirements
Technical requirements
Administrative functions
Typical nonfunctional requirements include the following:
Performance
Security
Capacity
Availability
Manageability
Recoverability
When identifying and defining the requirements, separate the functional requirements from the nonfunctional requirements. Nonfunctional requirements are design constraints and will be documented separately.
The design constraints are factors that restrict the options the architect can use to satisfy the design requirements. Once the functional and nonfunctional requirements have been identified, they are separated. The nonfunctional requirements that define how requirements must be satisfied become the constraints on the design.
Design constraints include the following:
Technology constraints such as hardware vendors, software solutions, and protocols
Operational constraints such as performance and accessibility
Financial constraints such as budgets
Unlike functional requirements, the constraints and nonfunctional requirements may change during the design process. This holds true especially if the constraint introduces risks into the design. For example, if an identified constraint that requires a specific model of hardware to be used prevents the design from satisfying a functional requirement, the constraint may need to be changed or adjusted.
Assumptions are made by the architect and have not yet been validated. Assumptions are not accepted as a fact until they have been validated. As part of the design process, each assumption needs to be validated as a fact. If an assumption cannot be validated, a risk will be introduced into the design.
Any assumptions that are made will need to be defined and documented as follows:
Identify any assumptions that have been made about the design
Document the design assumptions
Common assumptions relate to power, space, and cooling. A common example of an assumption that an architect may make is as follows:
There is sufficient power, cooling, and floor/rack space available in the datacenter to support both the existing and consolidated environment during the migration
When working through the physical design, the power, cooling, and space requirements will need to be identified and the assumption validated. A goal of this project is to consolidate...
Risks include anything that may prevent the design from satisfying the requirements.
Design risks include the following:
Technical risks
Operational risks
Financial risks
Risks are often introduced through constraints or assumptions that have not been proven. Risks resulting from assumptions are mitigated by validating them.
Throughout the design process, design decisions should mitigate or minimize risks by following this process:
Identify any risks associated with the design requirements or assumptions.
Validate assumptions to reduce the risks associated with them.
Determine how design decisions will help mitigate or minimize risks.
There are a few risks in the design based on the discovery information, assumption, and constraints.
As part of the discovery process, the following risk was noted:
Currently, there is no shared storage. The current system and infrastructure administrators are unfamiliar with the shared storage concepts and protocols...
The conceptual design is created with the documentation of the requirements, constraints, and assumptions. The design documentation should include a list of each of the design factors. The conceptual design guides the design. All logical and physical design elements can be mapped back to the conceptual design in order to provide justifications for design decisions.
To create the conceptual design, follow the given steps:
Use the design factors to form the conceptual design.
Organize the design factors to be easily referenced during the design process.
Create high-level diagrams that document the functional blocks of the design.
The conceptual design should include a brief overview that describes the key goals of the project and any factors that may drive the business decisions related to the project. The conceptual design includes all the identified requirements, constraints, and assumptions.
The following paragraphs explain an example...
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