On Tue, Mar 10, 2009 at 02:38:31PM -0500, Harry Putnam wrote:
> > Could you move(mv) the clone to a new disc and boot it up? Or does
> > the COW kick in during mv... I'm not clear what happens.
>
> BZZZZZT => wrong:
As others have answered this is all about ZFS, and much has been written
elsewhere about ZFS. Suffice it to say that the COW stuff happens on
every write to the ZFS pool, and that you can't separate ("move") ZFS
filesystems and snapshots from the pool they are in.
> > Similar with the `snapshot'. It sounds like an OS frozen in time when
> > the shutter snapped. But can you move it to a new disc and boot up?
>
> On further consideration I need to drop this about snapshot.. After
> all, applying the term to real photographic snapshots, one would never
> expect a real snapshot to have the capabilities of the subject of the
> snap.
>
> So poor analagy... deeply flawed.
If you think of a filesystem as a movie and a snapshot as a single frame
then the analogy works: the snapshot isn't of the things that appear in
the movie, it's a snapshot of the _movie_ itself at a given point in
time. And the TimeSlider (the Nautilus GUI for retrieving files from
ZFS snapshots) analogy works too.
> But what about `clone'? It seems my reasoning stands on that.
The word 'clone' doesn't seem to have much in relation to photography,
but certainly works. I've got a snapshot of a filesystem, now I want a
copy I can write to (ah, you need to know that ZFS snapshots are
read-only -- you don't write to them, you clone them instead and write
to the clones).
Nico
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