Earlier quoted context omitted.
"SSDs though, they just disappear from the bus when they fail" This isn't always true, and actually shouldn't ever be true - it's a particular failure mode you're seeing, and while it appears to be one common across a number of SSD controllers, it's still a pretty sorry fact that it happens. All SSDs (at least all not-complete-rubbish ones) report some kind of flash/media wearout indicator via SMART, which isn't nece…
With thousands of sata SSDs, I've seen one fail in a traditional fashion (some sectors weren't readable, otherwise mostly fine) and the rest of the maybe hundred that failed would just disappear from the bus. I don't monitor the wear out indicators, but from occasional looking, we're never near a significant fraction of the wear capacity. I'm very happy not to have anymore spinning disks in production, because the ss…
SSDs on the other hand ...
I use SSDs for caching (ZFS read cache and mirrored SLOGs) and I use them for mirrored boot devices in modern, production systems that should have a fast OS device.
But if I want a system to run forever ... if I am optimizing for longevity ... I use compact flash, even in 2016.
(yes, of course I set them to be read-only and disable swap)