[Server-devel] Western Digital hard disk data

James Cameron quozl at laptop.org
Tue Aug 13 21:14:42 EDT 2013

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

More information about the Server-devel mailing list