Hey I see that you found hd-idle.

Last time I tried to use it it wasn’t compatible with smartmon.

I would take smartmon over spin down every day of the week.

I’m gonna go out on a limb and assume the reason you have this problem with power is that you’re running a zfs/md-raid 5 or whatever. It may be a good idea to get away from that configuration. When you write a file to a 3 disk pool with parity, all three drives spin up. The details are a whole nother can of worms but the way that operating systems, busses and hbas interact with disks make this even worse.

I got away from that situation with a mergerfs/snapraid setup where my disks are jbod and writing a file to the pool only spins up one disk (with some caveats) and parity calculation is done at night as a snapshot all at once.

I do not think this saves power, although my power use has been very low in this configuration. I do think this saves drives, because snapraid is decently judicious with spin up/spin down work, amassing all the changes first then calculating what to put where and doing that all at once.

If your primary concern is power use and hard disk life, consider a ssd pool. The density and power consumption are why datacenters switched to them and why 3.5 racks are so cheap now in comparison.