[Server-devel] Western Digital hard disk data

[George Hunt]

James, et al,

Monitoring the transient voltage minimums, running on battery, not
charging, with 2 ethernet dongles as additional load I get the following in
my testing of WD external  "my passport" drive:

XO4 -- voltage droops to 4.51 -- spins up reliably
XO1.75 -- voltage droops to 4.56 -- spins up reliably
XO1.5 -- voltage droops to 3.97 -- does not spin up

On the XO1.5, when I used external powered hub, idle voltage was 5.2, which
drooped to 4.97 during spin up.

Then I used my newly purchased lab power supply to try to find the
threshold for the decision to spin up. When I adjusted it to 4.3, and my
meter registered a transient minimum of 3.96, it failed to spin up. When I
set the PS to 4.35, and the droop went down to 3.98, the drive spun up. I
judge that the threshold is pretty close to 4.0v.

George


On Tue, Aug 13, 2013 at 9:14 PM, James Cameron <quozl at laptop.org> wrote:

> What did the bus voltage do during these events?
>
> A HD would probably decide not to spin up if the bus voltage was out
> of spec.
>
> On Tue, Aug 13, 2013 at 02:00:31PM -0400, George Hunt wrote:
> > Hi all,
> >
> > Following James' suggestion, I put my fluke 186 multimeter in current
> mode on
> > the USB cable between the power source and the WD hard disk.  I was able
> to
> > capture a 1A current spike, and a ~ 3 second current transient of about
> 800mA
> > during spin up.  The idling current for the hard disk, while spinning,
> was
> > 230mA.
> >
> > The XO4, (sku306) did not reliably spin up the HD. In particular this
> failure
> > was almost 100% when the 430mA load of the ethernet dongle, and MR3020
> wifi
> > access point was hanging on the other USB port.
> >
> > I put the hard drive and wifi accessories on a powered "Plugable" model
> USB2HUB
> > AG7, which has an adapter rated for 3A, and experienced no failures,
> during
> > many startups.
> >
> > I am concluding that an external hard disk requires a powered USB hub.
> >
> > Other interesting measurements:
> >
> >   • The MR3020 wifi unit had maximum current spikes of 530mA with average
> >     current of 175mA.
> >   • The USB ethernet dongle had 230mA spikes with an average of 177mA
> and a
> >     minimum of 172mA
> >
> >
> > George
>
> > _______________________________________________
> > Server-devel mailing list
> > Server-devel at lists.laptop.org
> > http://lists.laptop.org/listinfo/server-devel
>
>
> --
> James Cameron
> http://quozl.linux.org.au/
>
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