=== 1. Check your drives capability and status.
= 1.1. APM
For displaying the Advanced Power Management (APM) status of your drives:
hdparm -B /dev/sd?
WDMyCloud:~# hdparm -B /dev/sd?
APM_level = not supported
APM_level = 127
/dev/sda is the WdMyCloud internal drive. In this case, it does not support APM.
/dev/sdb is the first USB drive. In this case, the APM is set to 127 (via /etc/hdparm.conf).
= 1.2. Standby spin-down
For displaying the spin-down capability of the /dev/sdb drive:
hdparm -I /dev/sdb
WDMyCloud:~# hdparm -I /dev/sdb
Standby timer values: spec'd by Standard, no device specific minimum[many lines]
In this case, the /dev/sdb drive supports standby (spindown).
=== 2. Try it out
You can try it manually with the command hdparm.
When the WdMyCloud will reboot, it will forget everything you did with hdparm.
(The WdMyCloud applies the /etc/hdparm.conf settings when booting.)
Display hdparm help:
WDMyCloud:~# hdparmhdparm - get/set hard disk parameters - version v9.39, by Mark Lord....
-B Set Advanced Power Management setting (1-255)
-S Set standby (spindown) timeout
Try it out:
WDMyCloud:~# hdparm -B 126 /dev/sdb
setting Advanced Power Management level to 0x7e (126)
APM_level = 126
The disk will go ‘power management’ after 126 x 5 seconds of inactivity.
Max value for spin-down = 127.
Try the other one:
WDMyCloud:~# hdparm -S 179 /dev/sdb
setting standby to 179 (14 minutes + 55 seconds)
The disk will spin-down after 179 x 5 seconds of inactivity.
Your disk must support at least one:
either -B (APM),
either -S (spindown).
Notes about hdparm:
-y Put drive in standby mode
-C Check drive power mode status
=== 3. Inactivity
Finally, you must make sure that the USB drive actually remains unrequested.
Nothing should read or write that disk for a while.
Here are my settings in the http://wdmycloud interface:
cloud access off
energy saver on
mac backups off
With hdparm.conf set and all those services enabled, my USB drive spun down for short times, but it was frequently woken up.
Turning the services off made the difference.