Mailinglist Archive: opensuse (856 mails)

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Re: [opensuse] Reliable way to backup hard drive before clean install
Quoting Per Jessen <per@xxxxxxxxxxxx>:
Carlos E. R. wrote:

On 2016-10-04 11:47, Per Jessen wrote:
Carlos E. R. wrote:

On 2016-10-04 08:14, Per Jessen wrote:
John Andersen wrote:

On 10/03/2016 11:59 AM, Carlos E. R. wrote:
Reason: a few (or
one) byte error makes the tar unrecoverable.

In reality, Carlos, exactly how many of these have failed for you?

Yes, I have to wonder that too.

It is rare, but it is documented. Media failures are possible, and
if one happens in the middle of a tar.gz you lose it completely.

Sure, but every archiving tool is vulnerable to media and network
failures, tar no more so than any other.

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.
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.

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

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