>They're unlikely to die just sitting there without power Actually they will likely die shortly after you use them again. HDDs have bearings and they are lubri

>They're unlikely to die just sitting there without power Actually they will likely die shortly after you use them again. HDDs have bearings and they are lubricated. The lubricant ages and might even collect at the lowest point in the bearing. Once the disk is powered up after many years the bearings will no longer be properly lubricated they get warm expand and destroy themself. The HDD could run for a few minutes or several hundred hours before it starts to make weird sounds and vibrations and turn itself off to prevent further damage or it keeps going until something dies (common for older models). >multiple redundant copies should cover any issues with single-device failure. Certainly needed but in the end its probably not worth the time. I would need dozens of such disks to get the few TB in backup space that I need. BTW fans in PCs and laptops die for the same reason as described above. Its common for old laptops to make weird noises and overheat after they where left untouched for years.