Re: Independent failures?
Presumably the calculation is that each RAID-Z3 array will spend N hours each year degraded/rebuilding, then calculated how many years it would take before a further double-disk failure occurred during one of those windows of vulnerability, to get a nice impressive number. Nice bit of benchmarketing, but not remotely realistic of course.
(I preferred the guy - from Intel, IIRC - going through disk reliability figures, pointing out that with a modern drive capacity approaching 10^14 bits, suddenly that "good" error rate of 10^-15 becomes a virtual guarantee that you *will* hit corruption at some point while rebuilding your RAID 5 array - so you need a minimum of RAID 6 just to be able to rebuild an array of large drives reliably. Meanwhile, a scary proportion of our data isn't checksummed, so when it does get corrupted we won't know about it until it's too late!)