[Linux-cluster] Snapshotting GFS and freezing

[Pasi Kärkkäinen]

On Thu, Jan 14, 2010 at 02:57:03PM -0500, Jeff Sturm wrote:
> > -----Original Message-----
> > From: linux-cluster-bounces at redhat.com
> [mailto:linux-cluster-bounces at redhat.com]
> > On Behalf Of Dirk H. Schulz
> > Sent: Thursday, January 14, 2010 12:21 PM
> > To: linux clustering
> > Subject: [Linux-cluster] Snapshotting GFS and freezing
> > 
> > Hi folks,
> > 
> > I found several howtos on the web stating that if you want to snapshot
> a
> > gfs volume (on top of clvm, of course), you have to freeze gfs (using
> > gfs_tool) to make that possible.
> > 
> > What comes in mind then is: If I have to freeze the gfs volume anyway,
> > do I need a snapshot at all? Can't I copy the contents off the frozen
> > gfs volume directly?
> > Because the basic purpose of a snapshot is to provide files that do
> not
> > change during beeing copied. And I would expect a frozen gfs volume to
> > provide exactly that.
> 
> The important consideration here is:  How long can you withstand the
> filesystem being frozen?
> 
> You can freeze it, copy all files (e.g. with rsync) and unfreeze,
> potentially over the course of a few hours.  If that's okay with your
> application and users, go right ahead.
> 
> Or you can freeze, snapshot and unfreeze, and potentially be done within
> a few seconds.  That's the beauty of snapshots--we do it online with
> little or no user disruption.
> 

Hmm.. so snapshots with CLVM are possible nowadays? 

-- Pasi