@Jimmy9008 keep in mind that resulting availability and risk aren't the same thing. Any five nines system is expected to hit six nines nine out of ten years. It's the average over the operating lifespan, not over a set interval. Otherwise any normal interval that you select would have 100% uptime.
So there are two ways to look at it reasonably...
Resulting Availability Over Operational Lifetime
Expected Availability Over Operational Lifetime
The first is what an individual system actually provides. The second is the average of all systems configured identically, over all of their operational lifetimes.
The first you measure. The second you project with simulations.
In extremely large systems, like BackBlaze, they get close approximations to the later through measurement because they look only at small components (like hard drives) of which they have substantiation numbers to create a reasonable approximation to a full number.
When I was on Wall St., we had 80,000 servers in our pool and so we had actual risk and availability numbers for the industry in datacenters like ours. But it still only told us about a handful of server models, and only under our exact conditions. And it still took a decade or more to produce meaningful numbers, and those numbers only applied to the servers of the past, not the ones being installed new.