Availability as the Most Significant Contributor to TCO
Our experience with information systems has shown that the user requirement responsible for the greatest hidden costs is availability. This user requirement takes precedence over all otherswhat good is a system if it's unavailable? It also requires ongoing management and maintenance throughout the entire life of every system.
A system is available when users can work with it without experiencing outages. Note that as long as a user doesn't perceive or feel an outage, the system is considered to be available; availability is measured from the user's point of view. A user will consider a system unavailable in the following circumstances:
The system is not accessible. If the user can't access the resources needed to run an application, the system is considered to be unavailable. The system is equally unavailable if all workstations or software licenses are in use, or if the network connection to necessary data is down, or if the system has a virus infection.
The system is too slow. The system may be operational, but if the response time is long the user will give up waiting and consider the system as unavailable.
The system is intermittently having problems. The user will choose not to use a system if he or she suspects work may be lost due to intermittent system failures.