On Thursday 13 May 2010 15:34:04 Paul Davis wrote:
> I assume (as I am not an expert in the area) that the difficulties in
> overwriting blocks on a tape is due to the inaccuracies of the medium
> when writing to the exact location? Or is this simply a matter that
> neighboring data on the tape might be affected by the non-equal
> treatment of the tape itself?

It is more a question of the second of the above.  A tape is made to append 
to.  You can read at random blocks, but you cannot reliably write random 
blocks, without damaging following blocks.

>
> If I were to migrate the tape, the suggested procedure would involve the
> spooling of the entire ~650-700GB to a drive, selectively editing the
> files, and then rewriting the lot to a new tape with the old label? Is
> there any way to code this using the existing tools?

Bacula will do tape to tape migration.  For more on that, please see the 
bacula-users list.  We only deal with development and possible bugs, and 
sometimes wierd technical questions :-)

Kern

>
> > Hello,
> >
> > To the best of my knowledge, it is not possible to selectively overwrite
> > records in the middle of a tape.  Doing so, will almost surely also
> > destroy some data you wish to keep.
> >
> > You would be better off simply migrating all the jobs you want to keep
> > then demagnetizing or erasing the old tape.
> >
> > Best regards,
> >
> > Kern
>
> Thank you,
> Paul Davis



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