Re: Mdadm server eating drives

[Stan Hoeppner <stan@hardwarefreak.com>]

On 7/3/2013 2:47 PM, Barrett Lewis wrote:
> I added the two non-fresh drives back to the array and they have been
> resyncing.  The first one is almost complete.  No errors so far.
> Everything is been very smooth since replacing the power supply.
> And I am paying extra close attention to make sure my TLER capable
> drives have it turned on, and the others have the driver timeout set
> to 180.  From now on I will only be buying TLER capable drives.
> Just an update.

Good to hear.  I hope things keep looking up.

> Also, this is likely the same drive making the same noise with the top
> off https://www.youtube.com/watch?v=a9i5yixsJbk
> I wonder if its PWM driving the actuator against the barrier.

Spinning HDDs use voice coil actuators to move the head.  The voice coil
is driven by direct DC current, not pulse width modulation.  PWM
generates constant voltage and current but cycles the circuit hundreds
or thousands of times per second.  The lower the frequency the less
power to the device.  The higher the frequency the greater the power.
Thus PWM is suitable for varying the speed of brushless DC fans and the
brightness of incandescent light bulbs.  It simply won't work for
driving voice coil actuators.

Regarding HDD noises, identifying/diagnosing them is a voodoo science,
unless you happen to be an engineer at Seagate, WD, or Toshiba, which
are, sadly, AFAIK, the only 3 remaining HDD vendors left on the planet.
 Seagate and WD have swallowed all the others.

-- 
Stan