Every cloud service provider and data center provides its customers with a service level agreement (SLA) that stipulates (among other things) the amount of time their systems will be up and running throughout the year. This is critically important for businesses that rely upon high levels of system availability to deliver their own products and services. A good SLA should cover a variety of factors, but none are more important than uptime reliability. Here’s where all those 9s of availability come in. Uptime reliability is generally expressed as a percentage that gets as close as possible to perfection. The more 9s of availability, the more time servers will be up and running throughout the year. An SLA downtime provision that promises 99.99% system availability, for example, is more reliable than one that promises 99.9% uptime.