[2256] in linux-scsi channel archive
Re: How to skip over tape eof mark
daemon@ATHENA.MIT.EDU (Andy Poling)
Wed Aug 6 16:34:58 1997
Date: Wed, 6 Aug 1997 12:57:17 -0400 (EDT)
From: Andy Poling <andy@realbig.com>
To: Louis Mandelstam <lma@sacc.org.za>
cc: linux-scsi@vger.rutgers.edu, glug@linux.org.za,
unix-wiz@listserv.nodak.edu
In-Reply-To: <Pine.LNX.3.95.970806102240.22960a-100000@sacc2.sacc.org.za>
On Wed, 6 Aug 1997, Louis Mandelstam wrote:
> I have a tape here (Exabyte 8mm) which had 'mt eof' (write eof
> marker) executed on it while the tape was wound to the beginning, when the
> user meant 'mt eod' (seek to end of data). Easy typo that turned out to
> be surprisingly lethal.
>
> I presume the first file will be lost (the first few bytes of it at least)
> but can anyone tell me how I can manage to get the st driver to skip over
> this boo-boo so that the rest of the tape can still be accessed?
Sorry, but I think you're SOL. It's the tape drive itself that won't ignore
the eof marker (which is really a filemark - FM). Or, more correctly, it
probably can't deal with the (now) corrupted block after the FM. Remember,
a tape drive is a linear access device. It really has no concept of random
access. Your linearity was lost when you (this is the "royal you" - i.e.
they) wrote that FM record over top of your data...
Also, most unix-like tape drivers automatically write two FM's and then
overwrite the second one when you add another tape file to the tape. Two
FM's means EOM to a tape drive. According to the st(4) manpage, under
Linux this depends upon the MT_ST_TWO_FM option setting.
If the data is really important, I'm sure there are companies who specialize
in pulling the bits off the tape using special drives that can ignore FM and
EOM...
-Andy
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