hdparmcommand to determine what is the current enter sleep mode timer value (APM LEVEL):
# hdparm -B /dev/sda /dev/sda: APM_level = 254The possible values for AMP level are between 1 ... 254. Multiply APM value by 5 and you get number of seconds your hard drive enters standby mode. For the block device /dev/sda above we can see that it enters standby mode after 1270 seconds of idle time that is if we set APM_level value to 1 the hard drive enters sleep mode after 5 seconds. 5 seconds may seem as a lot of energy saving, however, it may come with the price of reduced hard drive's life span.
# hdparm -B100 /dev/sda /dev/sda: setting Advanced Power Management level to 0x64 (100) APM_level = 100Now the hard drive we sleep after 500 seconds of idle time.