Persistent HDD APM settings

An HDD can be configured to spin down after a certain time via the APM settings which can be managed by smartctl. For example

sudo smartctl --set=apm,63 /dev/sdb

sets the APM (Advanced Power Management) level of disk sdb to 63, a fairly aggressive power-saving level. Note that APM controls how aggressively the drive manages power, not a literal spin-down timer; an actual idle timeout is configured separately, for example via hdparm -S.

Unfortunately, those settings do not persist after a reboot. To achieve persistence on systems with systemd installed, the following sdb-apm.service service file can be created in /etc/systemd/system/

[Unit]
Description=/dev/sdb apm settings

[Service]
ExecStart=/usr/sbin/smartctl --set=apm,63 /dev/sdb

[Install]
WantedBy=multi-user.target

After enabling the service with

sudo systemctl enable sdb-apm.service

the settings should persist even after a system reboot.