hard disk config parameters for use by hdparm are set up in /etc/sysconfig/harddisks, which are evaluated by the script /etc/rc.sysinit at boot.
Before to tweak with HD parameters, I strongly suggest to check the hard disk specifications provided from the HD producer. Particularly about power management, you should note that at least for laptop an always on is not the best, because of increased power consumption and increased heating.
Only change parameters when you know exactly what you are doing.
my 2 cents.
Thank you for your reply AS,
Regarding increased heating, I have actually monitored the HDD temperature and it does not seem to rise much, maybe 1-2 degrees C and it's well below max operational temp.
My thoughts on the APM settings are, since I'm mostly running the laptop on AC it could be considered to be a desktop computer. The head parkings are to protect the HDD from bumps and sudden movements, but since it's just sitting on my table it won't protect the hard drive from anything at all. The more parkings the more it will be wore down, most drives are guaranteed to handle 600 000 parkings/unparkings and by my rate I will reach that limit rather quickly. When I replaced my old drive it had sustained about 1 200 000 parkings/unparkings and was still fully functional (but to small to handle a triple boot setup).
As the laptop-mode.conf file suggests the settings should be different when on AC and when running on batteries and that's my view as well.
Just checked /etc/sysconfig/harddisks
, I didn't find anything that would set the APM value to 128 so I'm still wondering where that setting came from.
Edit: I'm using the command smartctl -a /dev/sda | egrep '(Load_Cycle_Count|Temperature)'
to monitor both temperature and load cycle count.