Spin down HDD after disk sync or before power off

Bernd Walter ticso at cicely7.cicely.de
Mon Mar 9 16:19:39 PDT 2009

On Mon, Mar 09, 2009 at 04:17:15PM -0600, Rick C. Petty wrote:
> On Sun, Mar 08, 2009 at 01:36:09PM +0100, Bernd Walter wrote:
> > On Fri, Mar 06, 2009 at 03:47:38PM -0600, Rick C. Petty wrote:
> > > On Fri, Mar 06, 2009 at 03:30:14PM -0600, Octavian Covalschi wrote:
> > > > Why is spinning down is bad for HDD ? I believe it's better to spindown a
> > > > drive,
> > > > instead of cutting power too sudden.
> > > 
> > > Comparing those two, I'd say it shouldn't matter (although probably a
> > > forced spindown may be better).  But pulling power from a drive does not
> > > mean the drive immediately stops doing stuff.
> > 
> > My understanding is that without power the heads just slamm into
> > landing zone, while it can be done in a controlled smooth way with
> > power.
> Nope, according to a coworker (whose wife works for an HDD manufacturer),
> the spindle motor is shunted and the generated electricity is used to
> properly land the head.  My coworker also tells me that some new drives are
> actually parking the heads off the disk, which as I understand is a much
> more difficult task since you have to worry about vertical separation when
> you bring the heads back between the platters.

The ramp load/unload thing is true:
Some drives also have the ramp on the inner side.

This highly disagrees with the loud clank noise that some disks are
doing on power loss.
The myth about generating emergency power from spindle rotation is
very old, but people from (other?) HDD manufactorers denied that.
The above document claims that their drives are also doing power
reclaiming from rotation.
Another used technology however is using the air current from the
rotation or a loaded spring.

> > > I was just saying spindown on disks is bad in the first place.  Sure, you
> > > might save some wear and tear on the bearings, but you risk problems with
> > > the heads on both spindown and spinup.  In other words, if you can avoid
> > > power-cycling your drives, they should last longer (in that you're less
> > > likely to destroy the heads).
> > 
> > This depends on the disks.
> > Desktop and especially mobile drives are designed to sustain more
> > spin downs, but are not designed for rotating a long time.
> > But of course if you intend to spin up directly after spin down it
> > might be bad for them as well, since it isn't really saving spinning
> > time.
> That may be; I know nothing about differences with mobile drives.  If this
> is true, I'd like to find some replacement 2.5" drives which are intended
> for continuous spinning.

There are a lots of drives available, the market first came up with
blade systems.
The unfortunate thing is that 2,5" for contiuous use are usually
high speed drives, which takes a lot of power, which makes them a
bad choice for 24/7 low power devices.

> > This is nothing, which should be done on reboot, but for halts it
> > might be reasonable to do.
> Not sure what you're trying to say here, but I am for the idea of
> issuing a spindown request if we know the power is to be cycled.  If
> spindown are issued for all halts, I hope someone makes that a kernel
> tunable.

I ment, that we shouldn't do this for shutdown -r.
In all other cases I asume that it can't hurt even if it is not required
for specific drives.

> What I was hoping is that someone could point me to the "spinup" command as
> I have a drive which does not spin up until it receives this command.  Any
> takers?

For CAM there is camcontrol start.
Not sure about ATA drives.

B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.

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