Saving More Power: Hard Disk Spin-down
After the CPU, your hard disk is your laptop's most power-hungry component. As long as it spins, it consumes power.
Linux's out-of-the-box configuration makes it nearly impossible to spin down the hard disk, as the operating system performs flushes every few moments. So, to successfully spin down the hard disk, you'll need two different tools: a script to set laptop_mode in the kernel and the hdparm utility.
The laptop_mode switch used to be all you needed to spin down the hard disk, but over time other settings have cropped up that must be changed as well. There are numerous laptop mode scripts available on the Internet, but you can download a handy one from
http://www.linux-mag.com/downloads/2...laptop_mode.sh. This particular script is handy because it works with both 2.4 and 2.6 kernels. Run the script using the options start or stop, and run it either at startup, say from /etc/rc.local, or only when going into battery mode.
Once you've enabled laptop_mode, set the hard disk spin-down threshold using the hdparm command. hdparm lets you set the spin-down timeout with -S, and allows you to check the status of the drive using -C. See the hdparm man page for specific information about the timeout values.
The hdparm command can be added to apmscript to automatically adjust the timeout when on AC and on battery. When plugged in, the command...
# hdparm -S 48 /dev/hda
... sets standby to four minutes, which is quite suitable for most laptops. When running on battery, the command...
# hdparm -S 12 /dev/hda
... sets standby to one minute. Depending on how fast your hard drive spins up and how critical your battery life is, you may wish to increase or decrease these values.
