Re: [Qemu-devel] [PATCH v4 0/6] Efficient VM backup for qemu

[Kevin Wolf]

On Thu, Feb 21, 2013 at 06:53:24AM +0000, Dietmar Maurer wrote:
> > How would VMA fit in if the backup block job took a BlockDriverState
> > destination and vmsave worked atomically with backup block jobs?  You could
> > have QEMU write to NBD server ports that a VMA writer process has open.
> > VMA would happen outside the QEMU process.
> > 
> > The benefit of doing this is that the backup block job becomes a 
> > general-purpose
> > command and QEMU is not directly involved in capturing guest configuration.
> > IMO the management tool is the correct place to orchestrate guest restore.
> 
> I am still not sure what you describe here exactly. But this looks like you 
> want to have
> an external backup server (NBD), and move the code out of qemu.
> 
> But NBD is not the only option. There are many backup tool/servers out there, 
> and
> you can easily write a BackupDriver for any of them. Using a fixed protocol 
> like NBD
> does not really have an advantage for me, as you can write a BackupDriver for 
> that.

I think the reason why Stefan mentioned NBD is that qemu already has an
NBD block driver, so if you can backup to a BlockDriverState, you get
this for free.

However, I don't think there's any reason why we couldn't have a regular
(write-only?) VMA block driver inside qemu that can be used for the
target BlockDriverState if you want to backup into a VMA.

Kevin