[Linux-cluster] Snapshotting GFS and freezing

[Ray Van Dolson]

On Fri, Jan 15, 2010 at 01:35:14AM -0800, Pasi Kärkkäinen wrote:
> 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? 
> 

No....

RH has stated (recently on this list) that patches exist to do it, but
it hasn't been a high enough priority for them to complete the work to
the point where it could be distributed to customers.

Ray