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Date:      Fri, 12 Mar 2004 00:01:23 -0500
From:      Bob Johnson <bob89@bobj.org>
To:        freebsd-questions@freebsd.org, lee@slaughters.com
Subject:   Re: incorrect super block
Message-ID:  <200403120001.24456.bob89@bobj.org>
In-Reply-To: <4051344E.2070304@slaughters.com>
References:  <4050D554.9090102@slaughters.com> <447jxqde1l.fsf@be-well.ilk.org> <4051344E.2070304@slaughters.com>

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On Thursday 11 March 2004 10:53 pm, lee slaughter <lee slaughter 
<lee@slaughters.com>> wrote:
> >There is no filesystem support for mounting gzipped tar files as
> >filesystems, so you'll have to use it as a raw device.
> >     tar -xzf /dev/acd1
> >should extract the data.
>
> no, i tried it with tar file. it got maybe 20% of way thru with
> unexpected eof.
>
> with tar.gz:
>   tar:  /dev/acd1: Cannot read: Input/output error
>   tar: At beginning of tape, quitting now
>   tar: Error is not recoverable: exiting now
>
> i just want to back up to a cd.

That should have worked.  It seems likely you actually do have an error 
on the CD.  Although burncd has been more reliable for me than the 
Windows CD burners I've used, it does rarely produce a coaster. Did you 
write it at higher than the rated speed of the blank disk?

Example of a test of this method (running burncd at low speed to make 
sure tar+gzip can keep up):

===
# tar -czf - temp/* | burncd -f /dev/acd0c -s 2 data - fixate
next writeable LBA 0
writing from stdin
written this track 3760 KB total 3760 KB
fixating CD, please wait..
#
# mkdir temptemp
# cd temptemp
# tar -xzf /dev/acd0c

gzip: stdin: decompression OK, trailing garbage ignored
tar: Child returned status 2
tar: Error exit delayed from previous errors
#
===

All of the unpacked files were identical to the originals according to 
diff.  The error message seems to indicate that tar pads blocks at the 
ends of files with characters that confuse gzip.

I also did a test that produced 148 MB of tar.gz file, and it unpacked 
fine (with the same error message).

- Bob



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