[ltp] hdparm -B 1 and Load_Cycle on Hitachi HTS541616J9SA00

[Henrique de Moraes Holschuh]

On Tue, 08 Jan 2008, Marc MERLIN wrote:
> I never really worried about it because I tought it caused the drive to
> spin down and spin back up, which I can definitely hear, but wasn't

Head unload cycles != spin up/down cycles.  Although no disk will spin down
without unloading heads first, you can unload heads with the disk spinning.

> Yet, I just ran this:
> gandalf:/etc/acpi# smartctl -A /dev/sda | grep Load_Cycle
> 193 Load_Cycle_Count        0x0012   047   047   000    Old_age   Always -       537975
> 
> and found out that I was very close to the 600,000 Load Cycle limit,
> after which some say drives can start to fail.

Well, Hitachi drives are rated to 600k load cycles on the spec sheet, but
you will notice that the SMART attribute is still far from alarming.  600k
is not a magic number.  Your drive may well survive way over 1M load cycles,
depending on many factors, including temperature.  Or it could die tomorrow,
the same way it could have died when it was still at 400k unloads...

> It looks like my /etc/acpi/power.sh, or something else is buggy, and 
> hdparm -B 255 was not being run when the power was restored, so my 
> Load_Cycle_Count went up every second, even when the laptop was plugged in.

The thinkpad firmware itself can pester the disk with HD APM commands, so
you really need to issue hdparm -B 254 (not 255!) at every AC state change,
and also after any sort of resume from sleep/hibernation, and device bay
hotplug events (for drives in the bay/dock/whatever).

> 2) a comment on https://bugs.launchpad.net/ubuntu/+bug/104535/comments/8
> says "Just to let you know: Hitachi uses quite special own technology to
> park HDD heads outside of magnetic disks area to a special parking ramp.
> This causes HDD heads not to suffer from parking - they're NEVER land on
> disk surface during parking. So, actually, Hitachi HDDs can handle a
> LOTS of starts\stops without any real problems"
> And I indeed have a Hitachi disk: HTS541616J9SA00

Yes, that's why it survives 600k unloads easily, instead of the older
industry standard of 300k unloads.

And head unloads on the ramp *flex* the head assembly arms, which *does*
stress the arms.  And the ramp itself gets its share of mechanical stress
and since it is plastic, it probably will get damaged slowly at every use.

> My questions are:
> 1) why was my load cycle going up so quickly without the disk spinning
> down?

Because it unload heads too often, in order to cut power to the linear motor
that moves the head assembly (and also to better survive shocks).

> 2) Given all the info above, is my disk almost dead?

It is not an young disk, but it is difficult to say whether it is almost
dead or not.

> 3) Any idea why Load_Cycle_Count would go up every second when the drive
> really did not seem to be spinning down and back up?

Yes.  It is unloading the heads, which has *nothing* to do with platter
spin cycles.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh