[Linux-cluster] CLVM and Snapshots?

[AJ Lewis]

On Tue, Aug 02, 2005 at 02:10:25PM -0500, Nate Carlson wrote:
> On Tue, 2 Aug 2005, Nate Carlson wrote:
> >I'm curious if it should be possible to take a snapshot of a filesystem 
> >sitting on top of CLVM (*not* a shared filesystem like GFS; something 
> >like XFS or ext3, but still on a shared block device). I recall trying 
> >it a couple weeks ago, and it failing miserably, but don't recall why, 
> >and figured I'd ask if it should work before experimenting again.
> >
> >If it should work, a few questions:
> >- Should I be able to create the snapshot on any node, or just the node
> > that is using the LV that I want to create a snapshot of?
> >- Is the syntax identical to normal linux snapshots?
> >
> >Thanks!
> 
> OK, decided to try it.. here's what I get:
> 
> xen1:~# lvcreate -L 1G -s -n snaptest /dev/XenSystemDisks/iron
>   Error locking on node nitrogen: Internal lvm error, check syslog
>   Aborting. Failed to activate snapshot exception store. Remove new LV and 
>   retry.
> 
> Error on Nitrogen:
> 
> Aug  2 14:09:05 nitrogen lvm[295]: Volume group for uuid not found: 
> doCTDCC376pE3g2JA35fNAieVNTWpAC1B3UIGOGQpn5Um5FcmPsa8yQPa0p9o9ZP
> 
> Nitrogen does not have access to the PV that this snapshot is on, which 
> could be part of the problem.

...yeah, you can't do this.  How is the node is managing the snapshot going to
know that blocks changed on the node with the origin?  You need cluster
snapshots, which aren't finished yet.  Do *not* do this - you will seriously
screw yourself over.  

-- 
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Red Hat                                    E-Mail: alewis at redhat.com
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