Mailinglist Archive: opensuse (856 mails)

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Re: [opensuse] Reliable way to backup hard drive before clean install
On 10/05/2016 07:42 AM, Carlos E. R. wrote:
On 2016-10-05 12:13, Anton Aylward wrote:
You seem to miss out on that "one bit" being correctable by CRC

No if the only thing you have got is the tgz archive. Again, this
problem is documented.

"behaves awfully:, "Gives a lot of hastle in doing a recovery" and "its too
difficult for me" and even "I don't know how so I don't believe it can be done"
are all common cases.

The thing is that in many cases it can be done. The bigger the file -- and
you're talking about doing whole filesystems, the less likely or the more hassle
it is going to be.

And anyway, since many of the files are likely to be compressed already, as JDD
points out, an error in them renders them unusable and that has nothing to do
with TAR or your compression algorithm. There would be little point in my
compressing /home/anton as whole file system; the BIG parts of that tree are
the music and the videos, which amount to over 80G, compared to the rest of the
tree that amounts to about less that 25G.

That being said, I use LVM and have a number of LVs and file systems to make
that 25G manageable for backing up onto DVD. The DVDs are then mountable as ISO
file systems and can be treated as archives to extract specific file or to do a
complete snapshot restore.

LVM lets me take snapshots to make the DVD from :-)

In terms of acheive the stated objective of find a "Reliable way to backup hard
drive before clean install" this sounds a good strategy.




Saying "it can't EVER" be done only needs one case of it being done to prove you
wrong.
http://www.gzip.org/recover.txt

Let us not forget, gzip work on single files, not groups of files. Plain old zip
(and pkzip) operate on groups of files and have the concept of the archive
built-in. When you're dealing with individual files the issue of CRC for
individual files rather than the whole archive changes the landscape.

Let us not forget that many are switchng to the use of XZ compressions for a
variety of reasons. It is a block compression algorithm and if there is an
unrecoverable error then only that one file wherein it occurred is affected, all
the rest are unaffected.

And finally..
Lets not forget that a CRC is not a checksum. A CRC is about error correction.




--
A: Yes.
> Q: Are you sure?
>> A: Because it reverses the logical flow of conversation.
>>> Q: Why is top posting frowned upon?

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