Life of a byte on the hard disk

  • Thread starter Thread starter Man-wai Chang ToDie (33.6k)
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Man-wai Chang ToDie (33.6k)

The hard disk stores a byte by some kind of magnetism.

If I don't touch that byte on the disk for a long time, would it
lose magnetism and hence that byte of information?

After how long would that happen?

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Previously "Man-wai Chang ToDie (33.6k) said:
The hard disk stores a byte by some kind of magnetism.
Click to expand...

Well, not quite. There is complex modulation, ECC codes,
and other things. Essentially the idea is correct, though.
If I don't touch that byte on the disk for a long time, would it
lose magnetism and hence that byte of information?
Yes.

After how long would that happen?
Click to expand...

Nobody quite tells. Component life of HDDs is 5 years,
according ro the manufacturers. So unless that specific
surface areas is bad (very rare today, all bad areas
are reliably mapped out), 5 years is not an issue.

Personally I would expect to see problems with
good writes not before 10 years. But that is just my
intuition. It could be longer.

There are things you can do to stretch the time until
magnetization is lost. Running a full surfacte scan
(e.g. in the form of a long SMART selftest) periodically
will have the disk recognize and rewrite potenially
problematic data sectors.

Arno
 
There are things you can do to stretch the time until
magnetization is lost. Running a full surfacte scan
(e.g. in the form of a long SMART selftest) periodically
will have the disk recognize and rewrite potenially
problematic data sectors.
Click to expand...

I am thinking to ghost the disk periodically
so as to re-magnetize the idle data files....
that means buying a hard disk of the same size,
but maybe faster.

I am not a hard disk engineer so I am not
conveying my ideas correctly. :)

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Man-wai Chang ToDie (33.6k) said:
The hard disk stores a byte by some kind of magnetism.
Click to expand...
If I don't touch that byte on the disk for a long time, would it lose magnetism and hence that byte of information?
Click to expand...

In theory, yes.
After how long would that happen?
Click to expand...

Far longer than we have had PC hard drives for, so it isnt clear exactly when.
 
Arno Wagner wrote in news:[email protected]
Well, not quite. There is complex modulation, ECC codes,
and other things. Essentially the idea is correct, though.


Nobody quite tells. Component life of HDDs is 5 years,
according ro the manufacturers. So unless that specific
surface areas is bad (very rare today, all bad areas
are reliably mapped out), 5 years is not an issue.

Personally I would expect to see problems with
good writes not before 10 years. But that is just my
intuition. It could be longer.

There are things you can do to stretch the time until
magnetization is lost. Running a full surfacte scan
(e.g. in the form of a long SMART selftest) periodically
will have the disk recognize and rewrite potenially
problematic data sectors.
Click to expand...

Now tell us, babblebot, what the point of that is when it still looses
its servo data and the drive won't be able to find your precious data,
however good and strong it may be.
 
If I don't touch that byte on the disk for a long time, would it lose magnetism and hence that byte of information?
In theory, yes.
Click to expand...

When the disc is being rotated,
it would subject itself to a field.

Would that mere rotation kill the byte earlier?

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and Farce be with you!
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When the disc is being rotated,
it would subject itself to a field.
Click to expand...
Would that mere rotation kill the byte earlier?
Click to expand...

Yes, but there are several orders of magnitude in
fild strength difference. It will not matter in practice.

Arno
 
Franc Zabkar wrote in news:[email protected]
Refreshing your data may get around that problem, if it is a real one,
but there would be no way for the user to refresh the embedded servo
information that was prerecorded at the factory.
Click to expand...

Let me quess, you came up with that all by yourself, right?
Here is John Navas's response to claims by Steve Gibson, the author of
Spinrite, that "magnetic patterns 'weaken' over time":
http://groups.google.com/group/comp.dcom.xdsl/msg/9aeee32323c2978e
Click to expand...

Navas is a just as opiniated as Gibson, lots of rhetoric.
Do patterns weaken? Yes and No. Read sensivity of the heads may worsen
over time, wear and tear (contamination) may have its effects on fly height
and writes may not be as strong as earlier in life, the overall effect is the
same: what may have been readable first may well not be later.

Is writing back data a refreshing of data? No, but rewriting a
weak sector to a different area may well be accepted as such.
It is not about the 'fresh'ness, it's about the (presumably) better
quality of the area where the data is 're'stored.

Oh, and what may be a cure in one incident can be a plague in another,
if the drive develops a fault in the write element:
once perfectly readable sectors may be unreadable after a rewrite (refresh).
 
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