On all the time or off every night?

[Brad Bussé]

I personally disable all energy savings management in my OS and RAID software, and shut down everything at night unless I’m leaving it to render, backup or scrub & parity check on the raid.

If you’re running Enterprise-class drives, leaving them running all night is not a concern really since they are specifically rated to run 24/7 operation. Consumer drives are not. Even with enterprise drives I shut down unless I have a reason not to.