small question about tape-based dumps

[Tim Judd]

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

> 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