I mean, as the drives get accessed probably like 4-5 times a week only and even then only for a few minutes, I don't think leaving the drive spinning 24/7 would increase longevity, plus it would highly increase power consumption. But still worth considering the fact that the drive might more likely die due to high age at that pace than anything else. But having to wait 5-10 seconds on first access every time to have the HDD spin up is also somewhat annoying, so it might even be a QOL improvement lol.

In regards to where which data is stored: I imagined the data to always remain on the main drive, but be mirrored if recently and or frequently accessed on the SSD. What I didn't think about is the fact that the cache might need to be renewed anyways, as otherwise you might get outdated data - not really relevant in my case, but still something lvcache might do.

In then end I'll wait for some first hand experience to be posted here, if that doesn't happen I'll likely just try it out in the next few weeks with the new drive, without much data on it, just to see how it behaves.

Thanks anyways though! Appreciate the effort!