RAID-6 is in no universe a RAID-5 successor. Simplifications of enterprise needs and risk tolerances and compromise acceptance is sophistry. It is telling enough that despite the bluster of some on Hacker News, major storage vendors (ergo - people who know much more than you) still make RAID-5 the default. Maybe they just haven't read the news.
Regarding the backup -- yeah, no kidding. That was the point. If the argument is "this is better because it can accept one more of countless possible failure modes", then "better" can continue indefinitely (why not 10 parity copies?) In the real world of compromise considerations there is a benefit return assessment that draws a line at a probability point.
It also sounds like many on here think you buy a box of disks and then make one universal logical volume on it (e.g. "if you have a spare why not just make it RAID-6?"). Because the spare(s) are usually universal, and you have many logical volumes encompassing RAID-10, 0, 5, 6, whatever the situation calls for.
Apparently you're new to the web forums and aren't aware that different posts from different people may display only partial views of varying opinions, conflating a couple of my answers to different questions as one happily, and putting in someone else's answers with it for good measure. I, for instance, made no comment in this thread about proper hot spare policy.
About RAID-5: some major storage vendors still use it for smaller arrays. Some other don't use it anymore (NetApp, DDN come to mind). The notion that RAID-5 isn't fit for arrays of large capacity drives doesn't come from me and is hardly new. You don't need any links as obviously you know all about this already.
I've set up my first terabyte SAN in the 90s back when it used to fill a whole rack, 9 GB micropolis drives where hot and SSA was the new interconnect, but I probably know less about storage than you.
Ah, the grizzled vet angle. The bit about me being new to the web is particularly adorable, especially given that I prefaced it by referring to other people (ergo, there was no confusion). When you have many logical volumes suddenly you can make choices like "does this necessitate the extra protection of RAID-6, given the compromises"? And people are making that choice to this day, and no one is saying "Oh look, there's RAID-6 which is the newer version of RAID-5 so it's my default choice".
Regarding the backup -- yeah, no kidding. That was the point. If the argument is "this is better because it can accept one more of countless possible failure modes", then "better" can continue indefinitely (why not 10 parity copies?) In the real world of compromise considerations there is a benefit return assessment that draws a line at a probability point.
It also sounds like many on here think you buy a box of disks and then make one universal logical volume on it (e.g. "if you have a spare why not just make it RAID-6?"). Because the spare(s) are usually universal, and you have many logical volumes encompassing RAID-10, 0, 5, 6, whatever the situation calls for.