Mailinglist Archive: opensuse (946 mails)

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Re: [opensuse] WD Green AV HD: rsync read errors mapping
On 31/08/17 15:27, Anton Aylward wrote:
On 31/08/17 07:51 AM, Wols Lists wrote:
Note that magnetism decays. If the drive has trouble reading something
in a test, it should transparently rewrite it behind the scenes, and if
that is the problem then it's fixed. No remapping or anything.

As I've said before, think of DRAM needing refreshing. And now drives
are packing so much into such a small space, if the sector next to yours
gets rewritten, some of the write can leak and damage your data. If that
happens ten or twenty times your data is now unreadable ... (okay, it's
a lot more reliable than that, but that's roughly what's going on :-)

LOL!

Roll on the days when we have sub-atomic data storage, using the spin of each
electron in orbit around each atom in a (probably) diamond (or other carbon
crystalline) lattice.

Does that mean you've invented the perfect laser-guided tightly-focused
magnetic beam that writes *exactly* where you want on the disk? And
magnetic media that only changes state when you want it to, and not when
subjected to stray magnetic fields?

Or am I simply describing that phenomenon, where writes get smudged and,
on the basis of "if you can't beat them join them" shingled disks
deliberately do exactly that.

If you write to track 10 on a shingled disk, it will overwrite most of
track 9, obliterate track 11, and probably take out track 12 to boot. By
design.

Okay, normal drives don't (want) to do that, but writing to track 10
will send stray magnetic field over 9 and 11, weakening the data. The
way to deal with that is to increase the gap between tracks, except that
manufacturers want to decrease the gap to increase the amount of data
they can store.

The result is that data stored on magnetic disk *will* slowly fade,
exacerbated by writes to neighbouring tracks. And yes, writes are
probably good for several years, but if you have lots of old files on
your disk that you haven't touched for years, there is a reasonable
chance they will fail to read.

Cheers,
Wol


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