hd-idle
Spin down external disks after a period of idle time. tldr-pages
On Linux
Linux
Start a service to manage hard drive spin down. By default hard disks will spin down after 10 minutes of inactivity
systemctl start hd-idleIdentifySpin down a disk immediately
hd-idle -t /dev/sdXIdentifySet disks to never spin down, then set explicit idle times (in seconds) for disks which have "sda" or "sdb" in their device name
hd-idle -i 0 -a /dev/sda -i 300 -a /dev/sdb -i 1200Identify