Gmail: Reliability and Availability

Step 9: Reliability and Availability Considerations

Step 8 asked what happens when a piece of this system fails. This step answers it.

The target is 99.999% uptime, meaning five nines. That leaves only a few minutes of downtime a year. Reaching it takes two things. The first is removing every point where one failure could stop the whole service. The second is planning ahead for disasters, rather than reacting to them. Here are the main strategies for both.

**Redundant instances, no single point of failure