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Re: growisofs writes unreadable dvd+rw

On Thu, 14 Apr 2005 12:05:24 +0200
Jean-Christophe Michel <jc.michel@symetrie.com> wrote:

> Sorry for my english being hard to understand.
> I was told that an error on a tar achive can make it impossible to
> restore a file from a non corrupted part of the archive. Is it true ?

* If you run tar without on-the-fly compression (-z) you can simply read
  all the archive up to the read error. After that it depends if tar can
  find the next superblock (or whatever it calls the structural
  metainformation). I tested this with deliberate data corruption
  halfway through the archive and hb quite mixed results. After that I
  found a tar-fixing utility that might help. 

* If you ran tar through gzip (-z) everything after the error is gone.
  tar pipes the whole data stream unblocked through gzip and gzip can
  not recover from a read error. 

* It might be slightly better to run everything through bzip2 (-j on
  recent gnu tars) as bzip2 automatically blocks and a read error in one
  block does not affect later blocks. I didn't try.

* I did try afio which runs each single file through gzip and was quite
  robust against a few changed bytes in data area  as well metadata.

  I don't think afio can handle incremental, but you have to feed it a
  list of files which could be a list of files changes since last
  backup time (find ... -mtime ...).



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