> but I thought it was advisable to power up spinning platter disks at least every so often, once a year say?
Is there a specific reason why you would need to do that? I'm not really aware of any.
> And where are you keeping this backup, same box?
This is ultimately up to you, depending on what kind of redundancy you deem necessary and whether you have multiple physical locations where you could store the said drives.
These days, hard drives probably scrub themselves periodically, looking for and rewriting sectors with high error correction error rates.
SSD’s definitely do this.
Even if hard disks don’t do this, mean time to repair is a crucial parameter in raid durability calculations. If you spin the drives up once a year, the mean time to repair is 6 months. Most raid systems are likely to lose data if it takes more than a few days to repair.
The ball bearings have lubricant that can shift over time due to gravity. And the metal parts might weld to each other over time if they are not moved.
I think the welding takes more than a year. The lubricant settling probably depends on the quality of the drive and the ambient temperature. And I guess the ball bearings would be pretty tolerant (since you only have to move them a little to get the lubricant on them again), it's more likely that the heads would stick.
Is there a specific reason why you would need to do that? I'm not really aware of any.
> And where are you keeping this backup, same box?
This is ultimately up to you, depending on what kind of redundancy you deem necessary and whether you have multiple physical locations where you could store the said drives.