Two metrics that determine availability:
MTBF (Mean Time Between Failures):
Average time system operates before failing. Higher is better.
MTTR (Mean Time To Repair):
Average time to restore service after failure. Lower is better.
Availability formula:
Availability = MTBF / (MTBF + MTTR)
Example:
MTBF = hours, MTTR = hour
Availability = / = %
Reducing MTTR often has more impact than increasing MTBF. Automate recovery.