Efficiency

While generally considered a subset of availability or performance, some aspects of efficiency do not quite fit in there. Efficiency could be considered the first step to improved availability and performance, which increases the importance of knowing how efficient your systems are.

Efficiency parameters will be more service-specific than others, but some generic examples might include Squid hit ratios and MySQL query cache efficiency. Other applications, including custom in-house ones, might provide other efficiency-measuring methods.