Uptime Information

Uptime is a measure of the time a service has been "up" and operational. It came into use to describe the opposite of Downtime (time when a service isn't operational). Availability refers to the ability for a user to access and utilize a service. The uptime and availability of a service is sometimes measured in "Nines," the critical metrics of reliability. "Six Nines" means 99.9999% availability, which translates to a total downtime of approximately 31.536 seconds per year. All the "Nines" are listed below.

  • Three Nines (99.9%)
  • Two Nines (99%)
  • Six Nines (99.9999%)
  • Five Nines (99.999%)
  • Four Nines (99.99%)

The following table shows the maximum allowed downtime for a particular percentage of availability and timeframe, presuming the service is required to operate continuously. SLA (Service Level Agreement) and/or TOS (Terms Of Service) often refer to monthly downtime in order to calculate service credits to match monthly billing cycles.

Six Nines99.9999%31.536S2.592S0.6048S0.0864S
Five Nines99.999%5.256M25.92S6.048S0.864S
Four Nines99.99%52.56M4.32M1.008M8.64S
Three Nines99.9%8.76H43.2M10.08M1.44M
Two Nines99%3.65D7.2H1.68H14.4M
Note: D=Day(s), H=Hour(s), M=Minute(s) & S=Second(s)
Note: For monthly calculations, a 30-day month was used.

Choosing A Service Provider

When choosing a service provider, a balance needs to be reached between uptime guarantee percentage and service costs. Typically, the higher the uptime guarantee, the higher the service costs. If you see a cheap service provider claiming 99.999%, 99.9999% or 100% uptime guarantees — proceed cautiously — claiming something and actually delivering it are two different things.

  • 99.8% uptime equals DOUBLE the downtime of 99.9%. That 0.1% difference adds up over time. In one year, 99.9% uptime = 8.76 hours of downtime while 99.8% uptime = 17.52 hours. For this reason, a 99.9% uptime guarantee is the minimum we would suggest when choosing a service provider.
  • No service provider will have 100% uptime in the long run. It simply doesn't happen. They may have zero downtime (100% uptime) for a few months, but sooner or later something will happen. There are simply too many factors involved (networks, power, equipment failure, software issues, human errors, etc) and not all of them are under the control of the service provider.

Requesting Service Credits

If you plan on requesting a full or partial service credit, please refer to your service providers' SLA (Service Level Agreement) and/or TOS (Terms Of Service) which is where the legal fine-print for uptime guarantees and service credits is usual located.

  • It should be noted that uptime and availability are not synonymous. A service can be up, but not available, as in the case of a network outage. Uptime guarantees typically guarantee the service is actually available and usable by the customer and not just up.
  • Scheduled (planned or announced) maintenance is typically not included in uptime guarantee percentage calculations. Again — when service providers calculate uptime, they typically do not include downtime caused by any scheduled maintenance.
  • When reviewing the SLA and/or TOS, carefully note how service credits are calculated. You might only be entitled to a service credit so small that it isn't worth the trouble. However, it may be a good time to look for a new service provider.
  • Act quickly, service providers usually have time limits for requesting service credits. These time limits can be as short as 24-hours so immediately contact your service provider, report the downtime and request whatever service credit you are entitled to.
  • Be prepared to present your case (i.e. have your facts and figures straight). The SLA and/or TOS typically spell out what "proof" of downtime a service provider will accept. This "proof" is usually under the service provider's control (e.g. their own internal and/or external monitoring services) so it can be a balancing act to get them to acknowledge a downtime event occurred.
  • Accept the fact that service providers usually have final say in determining if a service credit will be issued. If you had genuine downtime that should have earned you a service credit and your service provider rejected your request then you should definitely look for a new service provider.