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Donne Martin
2019-05-12 07:16:51 -04:00
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@@ -530,7 +530,7 @@ This topic is further discussed in the [Database](#database) section:
### Availability in numbers ### Availability in numbers
Availability is generally quantified by uptime (or downtime) as a percentage of time the service is available. Availability is often measured in number of 9s--a service with 99.99% availability is described as having four 9s. Availability is often quantified by uptime (or downtime) as a percentage of time the service is available. Availability is generally measured in number of 9s--a service with 99.99% availability is described as having four 9s.
#### 99.9% availability - three 9s #### 99.9% availability - three 9s
@@ -554,7 +554,7 @@ Availability is generally quantified by uptime (or downtime) as a percentage of
If a service consists of multiple components prone to failure, the service's overall availability depends on whether the components are in sequence or in parallel. If a service consists of multiple components prone to failure, the service's overall availability depends on whether the components are in sequence or in parallel.
###### In Sequence ###### In sequence
Overall availability decreases when two components with availability < 100% are in sequence: Overall availability decreases when two components with availability < 100% are in sequence:
@@ -564,7 +564,7 @@ Availability (Total) = Availability (Foo) * Availability (Bar)
If both `Foo` and `Bar` each had 99.9% availability, their total availability in sequence would be 99.8%. If both `Foo` and `Bar` each had 99.9% availability, their total availability in sequence would be 99.8%.
###### In Parallel ###### In parallel
Overall availability increases when two components with availability < 100% are in parallel: Overall availability increases when two components with availability < 100% are in parallel: