small question about tape-based dumps

Jerry McAllister jerrymc at
Fri Oct 16 21:38:25 UTC 2009

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 /

For second dump:     mt -f /dev/nsa0 rewind
                     mt -f /dev/nsa0 fsf 1
                     dump 0af /dev/nsa0 /usr

third                mt -f /dev/nsa0 rewind
                     mt -f /dev/nsa0 fsf 2
                     dump 0af /dev/nsa0 /var


when all done        mt -f /dev/nsa0 rewind
                     mt -f /dev/nsa0 offline

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

> With regards
> Stevan Tiefert
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