Downtime in SLA

Do you know that there is a difference between 99.99% uptime commitment vs 99.999% uptime commitment?

The additional “.9” accounts for extra 47 minutes uptime per year. 47 minutes seem little but it could potentially cause a business disruption that affect its revenue in the downtime window. For example, downtime in an eCommerce platform can cause the business to lose customers.

Uptime and Downtime are also known as System Availability. You will usually see this under application, cloud, and infrastructure SLAs. The vendors will also charge you more for the extra .9 availability.

Failure to ensure system availability as per the SLA can be used as a basis for contract cancellation.

Here is a table of uptime (availability) % vs downtime period:

System Availability %	Allowable Downtime Duration
90% system availability	36.53 days allowable downtime per year
99% system availability	3.65 days allowable downtime per year
99.9% system availability	8.77 hours allowable downtime per year
99.99% system availability	52.6 minutes allowable downtime per year
99.999% system availability	5.26 minutes allowable downtime per year
99.9999% system availability	31.56 seconds allowable downtime per year