[Server-devel] Western Digital hard disk data
quozl at laptop.org
Wed Aug 14 19:44:37 EDT 2013
Thanks, that all sounds reasonable.
It is not practical to make clear recommendations from these tests,
because of the number of dimensions in the phase space that have not
- how other external drives of the same model draw power and respond
to the bus voltage, (manufacturing variance within a batch, and
changes to components used in manufacturing for which tracking
information is not available to you),
- how other external drives of other models draw power and respond to
the bus voltage,
- how other XO-1.5, XO-1.75, or XO-4 laptops respond to the power
draw, (our manufacturing variable and changes to components used in
- how the environment temperature affects the results,
- how the aging of the hard drive mechanism changes the startup power,
- how the aging of the laptop changes the voltage droop.
While a powered USB hub may appear to be a solution, such a hub could
suffer from the same kinds of behaviour, and variance. It also adds
more dimensions to the phase space. It also adds one more source of
power drain in a remote system.
A reasonable qualification test could be written. Given an XO being
deployed as XSCE, with a sample hard drive, and a USB ethernet device,
adding a third USB load and test ten power cycles. You might also use
a variable current draw device to find the power headroom in the
system before failure to spin up.
You can construct a variable current draw device from a switching
voltage regulator feeding a variable resistor. Smoke might be
released if the power exceeds the maximum rating of the resistor or
There's probably something else I haven't thought of. Consider this a
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