[pve-devel] Snapshot questions

Dietmar Maurer dietmar at proxmox.com
Mon Sep 7 11:16:35 CEST 2015



> On September 7, 2015 at 10:58 AM Philipp Marek <philipp.marek at linbit.com>
> wrote:
> 
> 
> > > > Above container management toolkit 'pct' already supports drbd, and it
> > > > would
> > > > be really cool to have snapshots, so that we can make snapshot and 
> > > > snapshot backups ;-)
> > > The same should be easily possible for KVM, too.
> > 
> > Yes, but we do not need that for KVM backup purposes, because we have 
> > a better method with KVM.
> May I ask which one?

Yes, we use kvm block driver backup feature, together with our .vma backup
format. That way we can make 'snapshot' backups without generation snapshots
at the storage level.

http://git.qemu.org/?p=qemu.git;a=blob;f=block/backup.c;h=965654d5214121abc6e621a2c25fcbfb441b5c47;hb=HEAD

> > We do not want to modify the snapshot. We only want read-only access.
> Oh, okay.
> 
> 
> > > > We can extend the storage API with 'activate_snapshot_volume()' and 
> > > > 'deactivate_snapshot_volume()' if required?
> > > Well, perhaps.
> > > 
> > > Would that make the snapshot itself available for access? 
> > 
> > there must be a way toö access snapshot data -  else we cannot 
> > (obviously) make a snapshot backup. It is up to the storage driver to
> > implement that.
> > 
> > > What if the 
> > > snapshot data is accessible only on another node and not on the current 
> > > one?
> > 
> > Well, the storage driver needs to solve that problem...
> Okay, so we might need the activate_snapshot_volume() and 
> deactivate_snapshot_volume() calls, to make the snapshot data available on 
> the node calling the function.

OK, will add them later.



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