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Magnetic decay in modern hard drives.

4 New Member
When you back up data and leave them (on a hard drive) for a considerable amount of time, chances are that some bytes may get coorupted.
Therefore it is a good idea to rewrite a hared disk with stable data on it every now and then.
So I am looking for a software that rewrites a certain percentage of a drive every day, so that it is rewritten e.g. every 200 days (rewriting 0,5% of the drive every day).

Does anyone know of such a program?

The more one leaves on media that will get corrupted but are not read-once, the more interesting this procedure gets.
So as more and more data are "stable" on a hard drive (or in the future on an SSD), it becomes really important to make sure the data is preserved in its original state ...
Nov 5 '08
16 10684
5,000 Recognized Expert Expert
Best archival media is stone tablet...
Nov 7 '08 #11
Curtis Rutland
3,256 Recognized Expert Specialist
Yeah, but the read/writes are pretty slow...
Nov 7 '08 #12
424 Contributor
Best archival media is stone tablet...
Cave wall painting is pretty reliable too. Some clever Cro-magnons archived their holiday snapshots on the walls of the Lascaux cave 16,000 years ago and they're still intact. But it's hard to find a good cave nowadays...
Nov 7 '08 #13
4 New Member

Ok - sorry for the drag
By the way I bought DVD-R's from Tayo Yuden who are "guaranteed " for a 100 year lifespam.

So I'll look out for a new external drive before long ...
whatever the interface, 1TB is going below €100 these days, so what the heck.

Thanks for the help and I'll have a close look at the caves. Alternatively, as my wife is a painter and is experimenting making her own colors, I'll see to it they last a cuople of thousand years, but then the canvas should be good enough (papyrus is quite ok I suppose)
Nov 10 '08 #14
424 Contributor
I did a little searching on the details how how HDDs demagnetize. From what I can ascertain, it looks like it would take about 22 years (details below) for you to loose your data due to thermally-driven demagnetization if the hard drive were just sitting motionless at room temperature in a dark corner. In reality, this time will be a bit shorter because of mechanical vibrations and external magnetic fields arising due to everything from the motor of the hard drive itself to lightening storms 50km away. Still, (aside from the fact that the data is usually regularly rewritten anyway) in the end, the hard drive will fail long before it demagnetizes due to other wear-and-tear factors so you don't need to bother re-invigorating your data (technically this is measured as the Mean Time to Data Loss [ref0]).

The magnetic domains that store bits on modern hard disk platters are comprised of a large number of magnetic grains. Although the entire bit domain can have a varying degree of magnetization strength, a grain is either magnetized or not magentized. The time it takes for a grain's magnetization to flip or decay is determined by the Néel-Arrhenius equation.

Now, for Cobalt-Chromium alloy magnetic films typically used in modern hard drives, the energy barrier is Eb = 2 x 10^5 J/m^3 * V and grain diameter is 10nm diameter yielding a volume of roughly V= 5.24 x 10^-25 m^3 [ref1]. Thus, Eb/(kB*T) ~ 25 where kB=1.38x10^-23J/K is Boltzman's constant and room temperature is T = 300 Kelvin. With a typical attempt frequency of 1GHz [ref2][ref3], this leads to a decay rate of 10^9 * exp(-25) = 0.01 grains/s = 326000 grains/year.

Acceptable levels of signal decay vary depending on system design but typically range between 10-20% [ref4], so it would take (-1/326000)*ln(0.8) = about 22 years for an entire bit domain to get 20% weaker causing possible loss of data due solely to thermal demagnetization effects.
Nov 14 '08 #15
5,000 Recognized Expert Expert
This just became an article...
Nov 14 '08 #16
1 New Member
Hello, Sorry to re-update an old post. For windows there is a free tool just for this. (currently its free for home users only)

Jun 1 '14 #17

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