High availability and cost are directly proportional: the more available that you want a system to be, the more redundant equipment you must install. For example, a server with a single hard drive, power supply, and memory board has three individual single points of failure. If any of these components fails, the entire server will not be available. However, a server connected to a storage array network, or a server with a redundant array of independent disks

(RAID) installed can have a single hard disk fail and the system will continue to operate. One single point of failure has been removed. Availability can be increased by adding redundant components or by having spare parts nearby and the ability to install them quickly.

Describe a technical system (networks and applications are two examples, but there are many others) you are familiar with and all of its technical components (there should be at least six, but no more than ten). Explain in lay terms the approximate incremental costs involved in equipment and people to make a system increasingly more available. Use the Internet, Walden Library research, or your personal experience to estimate the costs. Choose at least three availability targets for your comparison. Examples of availability targets are standard business hours, 99.9% availability (acceptable down time for a single failure of approximately eight hours each year) and 99.999% availability (virtually no downtime).