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Re: [Qemu-block] [RFC] Intermediate block mirroring
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-block] [RFC] Intermediate block mirroring |
Date: |
Fri, 10 Apr 2015 10:56:23 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Thu, Apr 09, 2015 at 02:40:00PM +0200, Alberto Garcia wrote:
> On Thu, Apr 09, 2015 at 11:39:28AM +0100, Stefan Hajnoczi wrote:
>
> > > The goal would be to convert this:
> > >
> > > [A] -> [B] -> [C] -> [D]
> > >
> > > into this:
> > >
> > > [A] -> [B] -> [X] -> [D]
> > >
> > > where [D] is the active image and [X] would be a copy of [C]. The
> > > latter would be unlinked from the chain.
> > >
> > > A use case would be to move disk images across different storage
> > > backends.
> >
> > The simple solution to that problem is:
> >
> > Assumption: backing files are read only. (True in most cases.)
> >
> > 1. Copy the backing files using cp(1) or another method.
> > 2. Issue QMP 'change-backing-file' command so that [D] uses [X] instead
> > of [C].
> >
> > So it can be done today already.
>
> So do you think it would be better to implement this somewhere else?
> The code that I have for QEMU is quite simple, the actual algorithm
> doesn't change, it only needs to do the changing of backing files in
> mirror_exit().
I'll take a look at your patch series, maybe there are advantages to
doing it within QEMU.
Stefan
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