What do most companies consider an acceptable SLA nowadays?
Three 9s? Four 9s? Five 9s? Six 9s? Downtime is simply unacceptable?
To put it into perspective, below are the meaning for those SLAs:
- 99.9 (three nines) = 8 hours, 41 minutes and 38 seconds per year
- 99.99 (four nines) = 52 minutes and 10 seconds per year
- 99.999 (five nines) = 5 minutes and 13 seconds per year
- 99.9999 (six nines) = 31 seconds per year
- 99.99999 (seven nines) = 3.1 seconds per year
- 99.999999 (eight nines) = less than 1 second per year, which technically means 24/7/365 (100%) uptime
Not all downtime has the same impact though. Planned downtime during agreed upon hours has a much lower cost than unexpected downtime during the middle of the day (ask Southwest Airlines otherwise… ).
Luckily high availability is a crucial part of most applications today, lowering the risk of the ongoing operations which are necessary to keep the systems up-to-date, secured, optimized, etc…
What was the SLA for the applications, hardware, software, systems that you are responsible for this past year?!