There has been some talk those days on laptop hard disk lifespan. See, for example, what Pascal says about it.
So, after some investigation, I saw that on my laptop (Dell Latitude D420) the BIOS doesn't handle an APM value of 255. By default the startup scripts execute hdparm -B 255 /dev/sda (or other devices) and that actually sets the APM value to 128 (as given by hdparm -I /dev/sda | grep Advanced). (I'm using Ubuntu 7.10 -- the script I'm talking about is /etc/acpi/power.sh.)
On the other hand, using -B 254 seems to disable APM. So here's a way to do it, by default, on every boot:
- Add those lines to /etc/hdparm.conf:
apm = 254
- Make /etc/init.d/hdparm run at startup:
ln -s /etc/init.d/hdparm /etc/rcS.d/S07hdparm
And now the load cycle count reported by SMART remains stable. Which means that hopefully my hard disk will live longer.
Addendum: if you don't use SMART, you should. Install the smartmontools package, enable SMART on your disks with smartctl -s on, and read the smartctl(8) manpage. Optionally, enable the smartd monitoring daemon (via /etc/default/smartmontools).