[ale] what exactly does a long smart hdd test do?

[Ron Frazier (ALE)]

Hi Mike W,

(snipping to selected parts)

"Michael H. Warfield" <mhw at WittsEnd.com> wrote:

>
>I had SpinRite absolutely fall on it's face when I tried recovering a
>failed 200G drive for a photographer friend a few years back.  Its
>struggles to recover and rewrite a bad spot on track 0 of that drive
>resulted in the loss of roughly an entire cylinder.  The efforts it
>made
>to "repair" that spot on track 0 seemed to have caused the physical
>damage to be extended further along the track.  Given that a logical
>cylinders don't really map 1:1 to physical cylinders any more, I'm sure
>it was limited to the one physical head and SpinRite just managed to
>finish the job taking out that entire physical track for me.  The drive
>had failed, no question about it.  There were other bad spots
>elsewhere.

SpinRite could never cause physical damage to the drive unless physical damage already existed, or unless just exercising the heads caused them to crash.  Most likely, a particle of contaminant had gotten under the head or there was a slight bump in the surface or a vibration caused head contact.  I have read that thermal effects, mechanical wear and tear, and accumulation of lubricants can affect the flying height of the heads.  Once the surface is damaged, most likely, any software that positioned the head in that spot for a period of time would have caused similar damage.  I suspect there was some residue from the crash, and once the head was positioned there for a long time, and or repeatedly, the debris got dragged along the entire track and created further physical damage.  It is true that SpinRite will try to read a damaged sector up to 2000 times, by flying the heads in from different starting locations and at different velocities.  But, I would assume that the design theory assumes that you don't have physical damage, ie, that you won't damage the drive by moving the heads around.  It may be true that, if there is physical damage, that SpinRite's aggressive techniques are more likely to cause more damage than programs which are more tame.

>SpinRite would not have prevented this crash (I believe it had suffered
>a "soft touch" head crash in a critical spot) and by using it before
>trying to use dd-rescue, I made a bad situation worse.  Using dd-rescue
>afterwards and a number of rather inventive techniques like varying
>temperatures (I actually stuck the drive in a freezer several times)
>and

I strongly suspect that any other program, including dd-rescue, could cause the further damage you described if the head had crashed and if that software positions the heads over the damaged area.

Sincerely,

Ron


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Ron Frazier
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