Date: Wed, 1 Dec 2004 21:40:53 -0500 From: Ken Smith <kensmith@cse.Buffalo.EDU> To: Joel Hatton <joel@auscert.org.au> Cc: freebsd-stable@freebsd.org Subject: Re: 4.x can't read 5.x dump? Message-ID: <20041202024052.GA11786@electra.cse.Buffalo.EDU> In-Reply-To: <200412020048.iB20mhiP009447@app.auscert.org.au> References: <200412020048.iB20mhiP009447@app.auscert.org.au>
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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@cse.buffalo.edu
there, funny things are everywhere. |
- Theodore Geisel |
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