What is availability?

Availability is the percentage of time that some service or infrastructure is accessible to clients and is operated upon under normal conditions. For example, if a service has 100% availability, it means that the said service functions and responds as intended (operates normally) all the time.

Measuring availability

Mathematically, availability, A, is a ratio. The higher the A value, the better. We can also write this up as a formula:

A (in percent) = $\frac{(T o t a l T i m e - A m o u n t O f T i m e S e r v i c e W a s D o w n)}{T o t a l}$ ...