Disk Spin down
There is a probelm with disk spindown via hdparm, the problem is that you must address a disk as /dev/sdc , which changes in the case of USB media and other disks, even when you add slaves,
hdparm -Y /dev/sdb will spin a disk down instantly
hdparm -S 240 /dev/sdb will set this disk to sleep when idle for 20 minutes (5 second units here)
or adding at the bottom of the file /etc/hdparm.conf a section such as
spindown_time = 240
to make those changes persistent across reboots.
To check the status of a disk, here is what you do
hdparm -C /dev/sde
You could get one of the following results
When spun down…
drive state is: standby
drive state is: active/idle
Don’t make your disks spindown too often, 20 minutes is good for me almost in all circumstances.
If the disks don’t spin down, chances are that selftest is enabled…
Check if it is enabled with
smartctl -a /dev/sdb
if it reads
Auto Offline Data Collection: Enabled.
then you need to disable it with
smartctl –offlineauto=off /dev/sdb
then wait for them to finish (if a test is running) then spin down.