So to the grandparent comment, 6x 9's of reliability is unrealistic to guarantee as an SLA.

If you get better, awesome, but SLA? Too unrealistic.

Depends. You're only thinking of one half of an SLA, the metric, rather than the measurement period.

What's the SLA penalty vs the extra the customer is willing to pay? If I think I can achieve 6 x 9's on a monthly basis, but probably I'll only achieve it 10 months out of 12, I can offer the customer an SLA of 6 x 9's for 100 USD per month.

My penalty can be 50 USD for failing to meet, and then I as a supplier walk away with 10 x 10 + 2 x 50 USD = 1100 USD for offering something I knew I couldn't achieve (consistently).

Indeed, in the early days of Amazon S3, they failed their SLA every single month. And I got... a 10% refund every month.