Infrastructure availability and SLA
If you have had to deal with SLA (service level agreements) from your internal IT or an external vendor, the availability (uptime) is one of the first questions. This is a number usually presented as a percentage (usually 99.9%. Adding or removing a few 9 after decimal might not seem to matter much, but in reality it could. The table depicts the points: Total downtime (HH:MM:SS)
|Availability||Per day||Per month||Per year|
While a 99% uptime SLA might not be acceptable because it is still high (14 minutes downtime per day), paying for 99.999% uptime might be an overkill as well. The most common SLA numbers I have seen are 99.9% or 99.99% . Hysterically, though I have also seen 100% uptime SLA, but these companies are only asking for trouble for themselves, because I do not believe 100% uptime is practical even with every high availability algorithm and network architecture in place. Hopefully these numbers are useful when you have to decide next time.