Both have very different failure modes depending on what is failing. Controller / electronics failure tends to instantly brick either. Some hard drives experien

Both have very different failure modes depending on what is failing. Controller / electronics failure tends to instantly brick either. Some hard drives experience a single failure event that wipes out a bunch of sectors, but they work fine afterwards and if you overwrite the affected sectors those are back to being fine as well, because they are relocated. For other drives this is ongoing, were more and more of the drive becomes unreadable and even unwritable. I believe both of these are platter surface damage, the latter perhaps R/W head or amplifier degradation. Bearing and motor issues tend to make themselves known in advance, if you listen, but at some point it will stop spinning up or seize while running; instant loss (but a high chance of data recovery, since both media and controller are intact). For solid state drives a lot of the issues are firmware problems. Things like drives becoming very slow over time have been caused by things like imbalanced internal data structures. Some are media related, e.g. some drives experience slow reads on old writes, because the voltage levels have decayed which necessitates internal retries or slower read speeds. Things like SSDs failing to enumerate are probably controller issues. In my experience both can fail either slowly, with degraded performance, or fast and total. However, known-good SSDs (most of Samsung, Intel) tend to be very reliable. Good hard drives too.