Heat and vibration are the worst enemies of a mechanical HDD. Avoid these two problems, and half the battle is won already.
Regarding putting the drive into power save: I was under the impression that the drive experiences maximum mechanical stress when it starts to spin up and spin down (acceleration and deceleration respectively). So it might actually be a good idea to let it run continuously rather than start up/shut down frequently. Can someone confirm this?
I agree with the rest, especially chkdsk and defragmentation. Chkdsk is an underrated but often useful tool to check for filesystem errors.
Ofcourse, a defragmented drive has to do less work in the long term to read/write contiguous files compared to fragmented files, so that's always a good thing. Just stick a reliable automatic defragmenter on Windows rather than relying on the native utility, and you're good to go.
As for SSDs, sure, they're more reliable than mechanical HDDs in some ways, but if they experience material breakdown (crystal structure defects etc at the cell level) you can still lose the drive if I am not wrong.
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