Re: growisofs writes unreadable dvd+rw
On Thu, 14 Apr 2005 12:05:24 +0200
Jean-Christophe Michel <firstname.lastname@example.org> 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 ...).