There are two ways to increase the availability:

- increase the MTBF
- decrease the MTTR

If we took the three nines example above and made the MTTR only six minutes (0.1 hours for easy calculations) our availability would now be:

Figure 1. MTBF of 1000 hours, MTTR of six minutes.

which is 0.9999, or four nines — ten times better!