Hi all,

I'm writing to report that I have detected the "unload cycle bug" while 
running SL5.1 on my laptop. This "bug" has received some attention 
months ago when it was found in Ubuntu¹ and consequently featured on 
Slashdot².


----- SUMMARY -----

Some hard disk manufacturers ship their drives - especially laptop 
drives - preset with some aggressive power saving settings. These 
settings cause the hard disks to park their heads after a very short 
inactivity time.

This hectic parking/deparking activity dramatically shortens the disk's 
life.

Said manufacturers apparently take for granted that the OS will set more 
sensible power saving defaults for the hard disk. Linux distros often 
don't do this. So it's not exactly a "bug", rather an omission (even 
though it can be argued that this is not really "Linux's fault").


----- DIAGNOSIS -----

The continued parking/deparking is typically easier to detect on a 
laptop, where you might hear periodic "clicks" coming from the hard 
disk.

A more reliable way is to watch the output of the following `sh` command 
line, to be issued as root while your system is AC powered (as opposed 
to battery powered) and not performing disk-intensive tasks:

while true;do smartctl -a /dev/hda|grep Load_Cycle_Count;sleep 120;done;

If the last number is constantly increasing every 1 or 2 lines, your 
system is affected.


----- A SOLUTION -----

The command:

hdparm -B254 /dev/hda

changes the primary drive's (/dev/hda) power settings to "almost never 
park heads". A lower number *might* be desired when running on battery, 
and an ideal solution would include a way to change that number 
according to power source (I don't know yet how to do this).

For the moment, I suggest that the above command be put 
into /etc/rc.local to make sure it is executed at boot.


Best regards,
Andrea Remondini




----- NOTES -----

¹ <https://bugs.launchpad.net/ubuntu/+source/acpi-support/+bug/59695>
² <http://hardware.slashdot.org/article.pl?sid=07/10/30/1742258>