Re: I know this won't work, I just want to know -why-.
- From: Willem <willem@xxxxxxxx>
- Date: Mon, 26 Dec 2005 11:04:45 +0000 (UTC)
Claudio wrote:
) I am wondering about this error correction thingy all the time. I just
) can't believe it is really able to correct anything. I hadn't yet got
) the time to learn details about it or to run the huge amount of
) necessary tests to see it clearly, so please excuse, that what follows
) is what I believe, not what I know - inspite of this I hope i can be
) helpful here:
)
) In my opinion the error correction implemented in many archiving
) programs works only in case the errors detected are errors with a very
) well known characteristics determined from experience with
) characteristics of failures found on storage media. In other words, if
) the kind of error is not as expected, the corrected version of the file
) will be wrong and there is no chance to see it when the original file
) version is no more available for comparison.
You are very much mistaken. You may want to read up on ECC to relieve this
strange worldview. Or, alternatively, just believe that it works.
For example, audio CDs and CDROMs contain error correcting codes.
These codes are roughly the same as the ones in archiving software. They
can detect and recover from any kind of error, as long as there aren't too
many of them. (As in: a mildly scratched CDROM can be read without errors,
a badly scratched CDROM will generate read errors, and on rare occasions,
give garbled data.)
) Sending files larger than 2 GByte over a 10 MBit network I have already
) seen many times damaged files on the receiving side without any notice
) about problems during transmission - theoretically as good as not
) possible, but seen by me multiple times (I was not able to reproduce the
) behaviour, since if I 'succeeded' in getting file damaged over the
) network again, the wrong data were not in the same area of it as
) before). With newer network (100 MBit and 1000 MBit) versions the
) problem with transmitting large files seem to go away, but maybe to
) provoke errors it need only larger files (e.g. 200 GByte)?
)
) Anyone here who has seen files transmitted over the network which got
) damaged due to the way network transmits them and not due to detected
) problems during transmission or failures on storage media?
Not for some time. Ten years ago, there were a lot more problems.
Error detection works by adding some kind of hash. If the has has,
for example, 32 bits, then there is a one-in-2^32 chance for each packet
that contains more than one error to go undetected.
SaSW, Willem
--
Disclaimer: I am in no way responsible for any of the statements
made in the above text. For all I know I might be
drugged or something..
No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT
.
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