[Info-vax] Delete a file from a tape?

[jbriggs444]

On Oct 13, 6:21 pm, sapienzaf <sapie... at noesys.com> wrote:
> On Oct 13, 5:38 pm, gartm... at nonsense.immunbio.mpg.de (Christoph
>
>
>
>
>
> Gartmann) wrote:
> > Hello,
>
> > I have a tape with a few files (backup savesets). The last file on tape is
> > an incomplete saveset. Thus, I would like to delete this last file from the
> > tape. But OpenVMS 7.3-2 lists the file, asks for confirmation to delete and
> > finally refuses to do so. My next attempt was to recreate the saveset in
> > question via BACKUP with /REPLACE. Here I got:
>
> > %BACKUP-F-POSITERR, error positioning MKB200:[000000]13OCT09MAC358.BCK;
> > -SYSTEM-F-OPINCOMPL, operation is incomplete
>
> > Thus, how do I get rid of the incomplete saveset on tape without loosing
> > the previous savesets? Do I need to copy the contents of the tape to disk,
> > delete the incomplete file, initialize the tape and copy back the rest?
>
> > Regards,
> >    Christoph Gartmann
>
> > --
> >  Max-Planck-Institut fuer      Phone   : +49-761-5108-464   Fax: -80464
> >  Immunbiologie
> >  Postfach 1169                 Internet: gartmann at immunbio dot mpg dot de
> >  D-79011  Freiburg, Germany
> >                http://www.immunbio.mpg.de/home/menue.html
>
> You can't delete a file on tape.  You can overwrite it.
>
> After you $MOUNT /FOREIGN the tape drive, issue a $SET MAGTAPE/
> SKIP=2.  That will position the tape after the end of the second
> (good) saveset.
>
> You can then issue a $BACKUP/NOREWIND to generate the third and
> subsequent savesets.
>
> Yes, you must issue the $BACKUP/NOREWIND for all savesets which follow
> the first two good ones, and which you want retained.- Hide quoted text -
>
> - Show quoted text -

David Dachtera's instructions are much better.  If you were to $ SET
MAG /SKIP=2 on a foreign
mounted tape you'd be skipping past the HDR records on the first
saveset, skipping past the first saveset data and positioning at the
EOF labels on the first saveset.  Writing a tape mark there would wipe
out all but the first saveset and would blow away the EOF labels on
that saveset.  Not a very good move.

In the good old days (if I recall correctly) a $ BACKUP /NOREWIND
would start writing at the current tape position.  That behavior was
changed decades ago.  The current behavior is that $ BACKUP /NOREWIND
positions to the end-of-volume indicator (between the two tape marks
there) and starts writing the HDR records for the new safeset at that
position.  So any pre-positioning work that you do is wasted.