Mailinglist Archive: opensuse (856 mails)

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Re: [opensuse] Reliable way to backup hard drive before clean install
On 2016-10-05 04:13, Jeffrey L. Taylor wrote:
Quoting Per Jessen <per@xxxxxxxxxxxx>:
Carlos E. R. wrote:


Not tar. The problem is gz.

Oh? Well, then use another compressor. xz is good.


All compression types are vulnerable to a single corrupted bit making the rest
of the file unusable. Compression removes all redundancy. Unless there is
error correction (additional bits), flipping a single bit is unrecoverable.

Exactly.

But a pkzip archive is less vulnerable than a tar.gz archive, because
the corruption affects a single file.

Rar adds, on request, those error correction bits.

There is another open format that does similarly, but I don't remember
which.

Codes are variable length, so there is no way to know where the next valid
codes starts. JPEG uses periodic reset codes that lets decoding/decompression
to restart but everything between a corrupt bit and the next reset is lost.

Good idea.


Archives usually have a table of contents, so the most a single bit error can
corrupt is a file.

except that a tar.gz compresses the already tabled archive. A single bit
bad, and you can not recover the archive itself, so no table of
contents, nothing.


--
Cheers / Saludos,

Carlos E. R.
(from 13.1 x86_64 "Bottle" at Telcontar)

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