tcopy

[Jeff Vian]

On Wed, 2004-09-15 at 17:45, James Wilkinson wrote:
> Jeff Vian wrote:
> > Be careful.  AFAIK using the dd command to copy to a tape may overwrite
> > the tape formatting. This will not be nice if it makes the tape
> > unusable.
> > 
> > The OP said he used tar to create the tapes.  Why not use tar to copy
> > tape to tape? (and avoid potential problems with formatting of the tape)
> 
> This is good advice: use tar to check the consistency of the tapes.
> 
> The one thing that's been worrying me about this entire conversation is
> the possibility of data loss. It seems to me too likely that there is
> something about these tapes (or drives) of which we aren't aware, and
> that two or ten years down the line, the tapes are found to be
> unreadable because of problems now. 
> 

He made one other statement that follows with this thought.

He said he had put 18 images on the first tape.  Unless he did that by
creating a single tar image he would have had to use a non-rewinding
feature of the tape drive (and thus 18 separate tar images), and would
have to position it to each image for the extract.

> Tapes tend to be used for backups, which means that people tend to just
> use them for at most three purposes: backing up, restoring, and if
> you're lucky, some way of doing a basic integrity test [1].
> 
> But that means that if you're doing anything more, you're stepping
> outside the boundaries of most people's experience with tapes.
> 
> I'm sure the OP will be very aware of the need to check *all* the tapes
> he writes, and to make sure he can retrieve all the files. But I'm
> paranoid, and think you can't stress such concerns highly enough.
> 
> James.
> 
> [1] For example, at work, my backup scripts have an option to read the
> contents from the tape. Both tar and cpio have to re-read the entire
> archive to produce this, so I can be pretty sure that the entire
> archive is readable.
> 
> -- 
> E-mail address: james | 'Short for "Sic Transit Gloria Humanorum", which is
> @westexe.demon.co.uk  | Latin for "There goes the neighbourhood!"'
>                       |     -- Menno Willemse
>