I have a hard drive, which should go to standby automatically after 30 or 60 minutes.
I tried (3 minutes for testing):
# hdparm -S 36 /dev/sda /dev/sda: setting standby to 36 (3 minutes)
And it didn't work, even when there were no access for more than 5 minutes. Now I thought about some process accessing data, so I tested
# hdparm -y /dev/sda /dev/sda: issuing standby command
Drive went to standby and kept sleeping, as you can lookup with
# hdparm -C /dev/sda;date /dev/sda: drive state is: standby
Touching some file in the mountpoint woke it up as you would expect it.
Why isn't the automatic suspend working? As far as I understood it should even turn off the hard drive independend from the OS, as long as there is no access.