Nice. Yeah drives over 4 years is not a matter of if, but when. I think my record so far is an old WD Green drive that lasted about 6 years 24/7.
Sorry to rez the dead thread but I wouldn't be so harsh on old drives, especially ones as relatively young as 4 years! All drives, whether 1 day old or 10 years old are a matter of when, not if, so there's nothing magical about 4 years. That's only 35k hours if they were run 24/7, which isn't even that long in drive terms. In my opinion that just means they made it safely out of the infant mortality period and are now in the prime of their life, much less likely to spontaneously die than they were for the first couple years :) I use almost all used drives nowadays and most of the ones I buy have 40k+ hours on them before they get to me. My longest running drives that I bought new (both WD Greens, funny enough) are 11-12 years old with nearly 90k hours on them! In my opinion you'll lose a lot more drives in years 1-3 than you will in years 4-6, but I don't have anything other than anecdotal evidence on a few dozen drives to back me up so I won't argue that point too hard.
I will say that I built my older server in 2008, started with three 2TB drives and within a year or two expanded it to ten 2TBs with a hot spare. I've had 11 total drive failures in that server. Four in the first 1-3 years, two in years 4-6 and five in years 6-12. Again, not enough to mean anything statistically, just anecdotal. Strangely I had two failures on the same day in 2016 and two failures one day apart in 2019, those were exciting times! After my drives were out of warranty is when I started replacing them with used drives with 30k+ hours on them, so most of the drives in the system are now in the 60k+ hours range, with the two lucky "originals" just under 90k. Granted this is my backup server today. I replicate the main server to it once a week, but even in the main server I'm using all used drives with 50-55k hours on them. I have a lot of trust in drives that have proven they can run 24/7 for years on end :)