Dump questions

Polytropon freebsd at edvax.de
Sun Feb 21 18:23:09 UTC 2010

On Sun, 21 Feb 2010 20:52:31 +0800, Aiza <aiza21 at comclark.com> wrote:
> Polytropon wrote:
> > On Sun, 21 Feb 2010 11:42:50 +0800, Aiza <aiza21 at comclark.com> wrote:
> >> 1. Using the -L flag to create a snapshot of the
> >> live running file system.
> >>
> >> Does this mean that a complete copy of the file
> >> system is written to .snap directory?
> > 
> > No. The snapshot, quite incorrectly explained, is a saved
> > delta between the file system on disk at a given state, to
> > fixate further modifications (that are not included in the
> > dump, of course).
> > 
> Sorry, I read your words but have no clue as what you are trying to say 
> with that statement. As i understand 'delta' to mean, the difference in 
> file system content between a point in time 'A' and 'B' some point in 
> time later in the future. Now just what is snapshot recording between 
> point 'A' and 'B' and how does that apply to what dump is going to read 
> and write?

Oh, I see I did express a bit unclear.

The snapshot means that the filesystem's status of a
certain point in time - here: when dump is beginning
to run - is fixated in a snapshot file, representing
its exact content at time A. This representation is
subject to the dump. All further deltas after A are
not incorporated into the snapshot, and of course not
into the dump. This means that all changes after A
are lost if the backup is restored.

A welcome solution, especially when dumo + restore
are used to transfer system and user data, is to
first run dump and restore, and then use cpdup to
commit changes that took place during or right after
the dump to the target.

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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