Restoring damaged incremental XFS dump?

Restoring damaged incremental XFS dump?

[Felix E. Klee]

I wonder whether I should use xfsdump as a replacement for a more
traditional incremental backup solution centered around the TAR archiver
STAR.  The advantage of STAR seems to be that files can also be
recovered even if, for example, the level 0 dump is damaged.  After all,
one is dealing with TAR, a pretty transparent archive format. The
advantage of xfsdump is that it creates true snapshots.

So, what happens when the level 0 dump created with xfsdump becomes
damaged.  Will I still be able to recover some files?  What about files
from >0 dumps?

-- 
Dipl.-Phys. Felix E. Klee
Naunynstr. 2, 76530 Baden-Baden, Germany
Tel.: +49 7221 396961, Fax: +49 7221 396960, Mobile: +49 174 1386060
http://www.linkedin.com/in/feklee

Re: Restoring damaged incremental XFS dump?

[Timothy Shimmin]

Felix E. Klee wrote:
> I wonder whether I should use xfsdump as a replacement for a more
> traditional incremental backup solution centered around the TAR archiver
> STAR.  The advantage of STAR seems to be that files can also be
> recovered even if, for example, the level 0 dump is damaged.  After all,
> one is dealing with TAR, a pretty transparent archive format. The
> advantage of xfsdump is that it creates true snapshots.
>
I'm not sure what you mean by "true snapshots".
I wouldn't really call it snapshots as in what you could get if you
froze the filesystem etc..
But I presume you are meaning how it tries to store all the xfs
supported information including extended attributes, extended inode attributes,
holes, etc...

> So, what happens when the level 0 dump created with xfsdump becomes
> damaged.  Will I still be able to recover some files?  What about files
> from >0 dumps?
> 
Yes you will still be able to restore stuff.
However, it is in its own format so only xfsrestore will be able to do your
restoring.
Dumps are separated into what it calls media files which are meant to
be self containing. So damage to 1 theoretically shouldn't prevent restoring
from another media file.
Multiple media files are normally only used for tape (only 1 used for a dump
to a file).
And an incremental dump should also be able to be restored in isolation
and there are some QA tests (in xfs-cmds/xfstests) that test this.

--Tim

Re: Restoring damaged incremental XFS dump?

[Felix E. Klee]

On Tue, 12 Feb 2008 11:03:57 +1100, "Timothy Shimmin"
<tes@sgi.com> said:
> I'm not sure what you mean by "true snapshots". I wouldn't really
> call it snapshots as in what you could get if you froze the
> filesystem etc..

Oh, it does not freeze the filesystem - what a pity.  I recall someone
telling me that it does.  Seems like that was bad information or my
memory is failing on me.

> > So, what happens when the level 0 dump created with xfsdump becomes
> > damaged.  Will I still be able to recover some files?  What about
> > files from >0 dumps?
>
> Yes you will still be able to restore stuff. However, it is in its own
> format so only xfsrestore will be able to do your restoring. Dumps are
> separated into what it calls media files which are meant to be self
> containing. So damage to 1 theoretically shouldn't prevent restoring
> from another media file. Multiple media files are normally only used
> for tape (only 1 used for a dump to a file). And an incremental dump
> should also be able to be restored in isolation and there are some QA
> tests (in xfs-cmds/xfstests) that test this.

Thanks!

Felix

-- 
Dipl.-Phys. Felix E. Klee
Naunynstr. 2, 76530 Baden-Baden, Germany
Tel.: +49 7221 396961, Fax: +49 7221 396960, Mobile: +49 174 1386060
http://www.linkedin.com/in/feklee

Re: Restoring damaged incremental XFS dump?

[David Chinner]

On Tue, Feb 12, 2008 at 12:17:15PM +0100, Felix E. Klee wrote:
> On Tue, 12 Feb 2008 11:03:57 +1100, "Timothy Shimmin"
> <tes@sgi.com> said:
> > I'm not sure what you mean by "true snapshots". I wouldn't really
> > call it snapshots as in what you could get if you froze the
> > filesystem etc..
> 
> Oh, it does not freeze the filesystem - what a pity.  I recall someone
> telling me that it does.  Seems like that was bad information or my
> memory is failing on me.

Use dm-snap to create a snapshot and do the backup from that.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group