small question about tape-based dumps

[Jerry McAllister]

On Fri, Oct 16, 2009 at 08:43:26PM -0600, Tim Judd wrote:

> Replies inline
> 
> On 10/16/09, Jerry McAllister <jerrymc at msu.edu> wrote:
> > On Fri, Oct 16, 2009 at 11:13:21PM +0200, Stevan Tiefert wrote:
> >
> >> Hello list,
> >>
> >> one example: If I have three partitions and I want to backup every day
> >> these partitions, will I need 21 tapes?
> >>
> >> I ask because it seems it is not possible to place more than one dump on
> >> one tape, isn't it?
> >
> > You can easily put more than one dump on a tape if there is
> > room enough for them.   Check out the  mt(1)  command.
> >
> > Something like   mt fsf 1    will skip over the first dump file
> > so you can write the second.    mt fsf 2   will skip over two files, etc.
> > That is dump files, not files within the dump.   Each dump of a
> > filesystem is one file.
> >
> > If you need to restore, it is just the same.   The first dump is
> > the first file.  The second dump is reached by skipping 1 file
> > with the mt command, etc.
> >
> > I actually rewind and skip between each dump of multiples made
> > to the same tape.   I also use the no-rewind device for the tape.
> >
> > So first dump is:    dump 0af /dev/nsa0 /
> 
> I understand that this creates a dumpfile on nsa0, and as I understand
> tapes (which may be wrong, which I ask for clarification here)..  To
> mark a end-of-file to be able to fast-forward/rewind, why can't you
> use:
>   mt -f /dev/nsa0 weof
> 
> It's description in mt(1) says it writes the end-of-file mark at
> current position

You do not need to. dump alrady writes that when it finishes each time.
If you to that, you will get a second one at that location.

You do not need to do the rewind and mt fsf between each dump.  I just
do it to make it very clear to myself in my scripts what I am expecting
and that I am doing it right.

////jerry    
  
> 
> > For second dump:     mt -f /dev/nsa0 rewind
> >                      mt -f /dev/nsa0 fsf 1
> >                      dump 0af /dev/nsa0 /usr
> 
> So if we use weof,  would the 2nd dump then be:
>   dump 0af /dev/nsa0 /usr
>   mt -f /dev/nsa0 weof
> 
> > third                mt -f /dev/nsa0 rewind
> >                      mt -f /dev/nsa0 fsf 2
> >                      dump 0af /dev/nsa0 /var
> 
> And 3rd:
>   dump 0af /dev/nsa0 /var
>   mt -f /dev/nsa0 weof
> 
> > etc.
> >
> > when all done        mt -f /dev/nsa0 rewind
> >                      mt -f /dev/nsa0 offline
> 
> And I've never used offline, guess I'll start now.
> 
> > I have this all in a script that also writes an index file
> > as the first file on the tape.
> >
> > Of course if you are doing a change dump the dump command is
> > going to look more like:
> >
> >                      dump 1af /dev/nsa0
> > etc.
> >
> > ////jerry
> >
> >>
> >> With regards
> >> Stevan Tiefert
> 
> 
> 
> Thanks for any input!
> --TJ