What's the easiest way to do a backup and verify?

[Bob Johnson]

On Monday 14 March 2005 12:20 pm, Jerry McAllister wrote:
> > * Jerry McAllister [2005-03-14 10:30 -0500]
> >
> > >  > [...] So then wouldn't a second dump of the same snapshot diffed to
> > >  > the tape device be a good for a verify?
> > >
> > >  No, because the condition of the files that you are dumping the second
> > >  time is different from the first time.
> > >
> > >  Most places cannot afford to make file systems completely unavailable
> > >  for periods of time long enough (several hours, up to a couple of
> > > days) to allow dump to be run twice without any changes being made to
> > > the file system.

In FreeBSD 5.3 a snapshot can be created in parallel with a live filesystem.  
There is no need to stop normal operation while doing a backup of the 
snapshot (if I understand it correctly). 

Whether different files are consistent with each other (e.g. two database 
files simultaneously used by the same application)  if you do a snapshot of a 
live filesystem is still likely to be a problem.

> >
> > Note the OP's use of the word "snapshot". I think he is right! Or if he
> > isn't; it has nothing to do with the filesystem beeing changed, but
> > rather something to do with the way the backup is written to tape.
> > However, I do think snapshots could be used for exactly this.
>
> But, if he is writing a snapshot, then why is he using dump?
> I think he was using the word snapshot to imply the dump file.
> But, of course, I could be wrong.
>

I assumed that when he said "snapshot" he meant "snapshot", a frozen image of 
a filesytem  I.E. see
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/snapshots.html

And it seems to me that he's right.  Two dumps of the same snapshot ought to 
have no diffs, so you could check the tape against the snapshot before 
deleting the snapshot.

- Bob