254 or 255 both disabled my APM.
anyway, the best i found, IMHO, is to edit /etc/laptop-mode/laptop-mode.conf and change CONTROL_HD_POWERMGMT=0 value to 1, then reboot.
my Load_Cycle_Count and Temperature_Celsius remained to a reasonably low values. no frequent hard disk clicking.
254 or 255 both disabled my APM.
anyway, the best i found, IMHO, is to edit /etc/laptop- mode/laptop- mode.conf and change CONTROL_ HD_POWERMGMT= 0 value to 1, then reboot.
my Load_Cycle_Count and Temperature_Celsius remained to a reasonably low values. no frequent hard disk clicking.