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Re: [Qemu-block] [RFC] Intermediate block mirroring
From: |
Alberto Garcia |
Subject: |
Re: [Qemu-block] [RFC] Intermediate block mirroring |
Date: |
Thu, 9 Apr 2015 14:40:00 +0200 |
User-agent: |
Mutt/1.5.20 (2009-06-14) |
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().
Berto