4.x can't read 5.x dump?

[Joel Hatton]

Thanks Ken (and thanks to Paul, who replied with similar info),

I can appreciate this - I shouldn't have been, but I guess I was just
caught out by the change in the filesystem type and didn't realise that
dump depended so heavily on it. I can work around, so all is well. Sorry
about the double posting btw, I didn't expect my first one to make it to
the list.

cheers,
-- Joel Hatton --
Security Analyst                    | Hotline: +61 7 3365 4417
AusCERT - Australia's national CERT | Fax:     +61 7 3365 7031
The University of Queensland        | WWW:     www.auscert.org.au
Qld 4072 Australia                  | Email:   auscert at auscert.org.au

> On Thu, Dec 02, 2004 at 10:48:43AM +1000, Joel Hatton wrote:
> 
> > I'm backing up a 5.x machine at the moment with this command:
> > 
> > dump -0Lau -b128 -f - /var | gzip -2 | ssh FreeBSD4 dd of=aacd0s1f.gz
> > 
> > After the dump finishes, I try to read the file on the 4.x destination:
> > 
> > # gzip -dc aacd0s1a.gz | restore -ivf -
> > Verify tape and initialize maps
> > Tape is not a dump tape
> > 
> > I can scp the file back to the 5.x machine and it loads just fine, so what
> > gives? This type of failure is somewhat scary for me right now, given that
> > I may have to restore files to another destination that may not be 5.x
> > based.
> 
> This is, unfortunately, something that you should not expect to work
> for any *nix variant.  The dump mechanism of creating backups creates
> output that has "intimate knowledge" of the filesystem so that it can
> recreate that filesystem exactly as it exists on the disk.  As the
> filesystem itself evolves (has features added to it) the dump programs
> need to have their data structures change to accomodate the extra
> information that is now needed.  For example if in 4.X there were no
> ACLs but 5.X added ACLs then the dump program's data structures would
> need to be changed so it had the ability to store the ACL information
> in the output, and the restore program would need to be modified to
> look for that and do the right thing if it finds ACL information.
> 
> If there had been no filesystem changes between 4.X and 5.X then
> there would not be any need to change dump, and what you are trying
> to do would work.  But there were filesystem changes between 4.X and
> 5.X, so dump was changed, and now there is extra stuff in the dump
> images that the 4.X version of restore doesn't understand.  This same
> general principle holds for all OS's, not just FreeBSD.
> 
> If you need to be able to "restore" stuff from a 5.X machine on a
> variety of different platforms (4.X, or some other *nix) then don't
> use dump to create the images, use something like Gnu tar which can
> be made to understand the concept of incremental backups.  You do
> however run the risk of not being able to do a "perfect" restore of
> a filesystem if you use some of the more advanced filesystem features
> like immutable files or ACLs - the tar mechanisms of doing backups
> may not be able to record that extra information.
> 
> -- 
> 						Ken Smith
> - From there to here, from here to      |       kensmith at cse.buffalo.edu
>   there, funny things are everywhere.   |
>                       - Theodore Geisel |