The cables and how they have to be managed/positioned in a case. I've had panics over a drive failing when it was just the cable after I'd already replaced the drive, restored data, and ran tests on the old drive that turned out to be fine each time.
I have multiple home servers running ZFS and the first thing to check when encountering errors is the SATA cables. Those blue foil fan-out types are the worst from my experience.
