I wondered if there is any good reason not to spin down the harddrives on the LibreElec shutdown/reboot ?
I followed hints found in the internet and:
1) installed "System Tools" add on (to get hd-idle)
2) I created a shutdown.sh script at /storage/.config with the following content:
hd-idle -t sda
hd-idle -t sdb
hd-idle -t sdc
hd-idle -t sdd
and added executable permissions to the file:
chmod +x shutdown.sh
IMHO this could be a default behaviour.