> I bought some 3 & 4 TB WD Red drives around 2014, and they have all been going 24/7 with absolutely no problems at all. It may seem like they are running fin

> I bought some 3 & 4 TB WD Red drives around 2014, and they have all been going 24/7 with absolutely no problems at all. It may seem like they are running fine, but are they actually? Have you run a zpool scrub or equivalent? What happens with these old drives is that one dies and then you have to replace it, which is very hard on the other drives as the array is rebuilt. Then while the array is being rebuilt, another drive dies. It's better to replace drives when they are EOL (usually 4 years if running 24/7) rather than waiting until there is a problem.