Let’s say I have an external HDD with 4 TB of data, and I store it in the shelf.
There is no dust going into it, or anything.
I take it out from the shelf after 10 years, will it work perfectly in theory?
If not, what part can deteriorate and why?
Electrolytic capacitors can dry out for starters
In theory, it should work perfectly.
Some old, old drives had a problem where the spindle wouldn’t spin, a phenomenon known as “stiction.” Drives made in the last – maybe – 15 years seem to be immune.
One other remotely possible issue would be “bit rot.” That’s where the magnetic polarity of a single bit could change over time, often being influenced by neighboring bits.
I’d personally feel a lot more comfortable if that drive was an SSD, not a spinning/mechanical one. Seems (and this is mostly gut feeling) like more can go wrong with mechanical drives: lubrication, things “sticking” etc.