About
Availability is the (elimination|absence) of downtime.
Availability is when a system still work after a node (computer) failure.
Availability means that you can always read and write to the system.
Availability is a SLI resources metrics that shows the percentage of time that the resource responded to requests.
In the real world, there is no such thing as 100% availability. Highly available systems are defined in terms of 9s (99.9%, 99.99%, …). The more 9s, the better.
No system can guarantee availability.
Articles Related
High
A high availability requirement implies that the system must replicate data.
Function
Availability is a combination of:
- how often things are unavailable - MTBF (mean time between failures)
- and how long they remain that way - MTTR (mean time to recovery).
<MATH> \frac{MTBF}{MTBF+MTTR} </MATH>
Visualisation. See desmos calculator
<MATH> f\left(x,y\right)=\frac{y}{y+x}\left\{x\ge0\right\}\left\{y\ge0\right\} </MATH>