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 commandDrive went to standby and kept sleeping, as you can lookup with# hdparm -C /dev/sda;date/dev/sda: drive state is:  standbyTouching 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.
Hard disk not going to standby automatically
linux;hard disk;power management
Note that some drives do not implement this feature, even if the command passes. You may also need to reduce the Advanced Power Management level to 127 or less with hdparm -B 127 /dev/sda. From the man page:-B      Get/set Advanced Power Management feature...     values  1  through  127 (which permit spin-down), and values 128     through 254 (which do not permit spin-down).If all fails, you can write a small script that polls /proc/diskstats or /sys/block/sda/stat for the number of read/writes on the device and explicitly puts the drive in standby if they don't change over several minutes.  See the hd-idle utility.