Nines are not enough: meaningful metrics for clouds

The opening paragraph of the abstract does a great job of framing the problem:

When it comes to SLOs, the interests of the customer and the cloud provider are at odds, and so we end up with SLAs (Service Level Agreements) that tie SLOs to contractual agreements. If a provider consistently delivered service right up to the SLO limit however, it’s unlikely that customers would be very happy. Expressing available SLOs in terms of ‘nines’ also causes some issues: it hides the difference between many short outages and a few long ones, which is something many customers care about.

Source: blog.acolyer.org