question about backups

James Gray james at
Mon Oct 10 03:10:47 UTC 2005

On Monday 10 October 2005 12:26, Kenneth P. Turvey wrote:
> On Mon, 10 Oct 2005 10:26:45 +1000, James Gray wrote:
> > On Monday 10 October 2005 07:52, Gregory Piñero wrote:
> >> These are all good ideas. I'm personally using the tar method, but I
> >> can't figure out a good way to test that my tar file will actually
> >> work when the time comes ...
> >>
> >> Is there any safe way to do that?
> >
> > According to "man tar" the "-W" option will attempt to verify the
> > integrity of an archive.
> There is also the --compare option.  I've used this.  It will let you
> know of any differences between your backup and your current system.
> What it won't tell you about are files that are simply missing in your
> archive.

Which works fine, if you're backing up static files.  But if you shutdown a 
database to do a cold backup etc, the compare will always tell you the file 
system has changed etc.

It's a valuable switch when doing user directories etc though :)

I generally check the exit status of programs as they finish in shell scripts 
(especially backups) and combine the logic from that with various --compare 
-T -W etc switches as appropriate to make sure a backup was successful.

We also have a policy to pick a backup tape at random once a fortnight and 
attempt a restore to a test partition.  This is a procedural thing (as 
opposed to technological) but is a valueable double-check.  IMHO, backup is 
as much about policy as it is about technology.


"Lead us in a few words of silent prayer."
-- Bill Peterson, former Houston Oiler football coach

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