Approximately 40 PB raw storage in our datacentres here, half of them Supermicro servers with whatever disk that came, half HP Proliant with $$$ HP Enterprise class disks, all < 5 years old, so quite comparable to the Backblaze situation.

80% drives surviving after 5 years seems right, this is what we're seeing as well. The hardware is decommissioned faster then the drives fail.