Re: [Qemu-devel] [Qemu-block] [RFC PATCH V4] qemu-img: make convert async

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Fri, Jun 01, 2018 at 07:16:14PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> 20.02.2017 17:59, Peter Lieven wrote:
> > Am 20.02.2017 um 15:50 schrieb Stefan Hajnoczi:
> > > On Fri, Feb 17, 2017 at 05:00:24PM +0100, Peter Lieven wrote:
> > > > this is something I have been thinking about for almost 2 years now.
> > > > we heavily have the following two use cases when using qemu-img
> > > > convert.
> > > > 
> > > > 
> 
> [...]
> 
> > > Does this patch work with compressed images?  Especially the
> > > out-of-order write mode may be problematic with a compressed qcow2
> > > image.
> > 
> > It does, but you are right, out-of-order writes and compression should
> > be mutually exclusive.
> 
> 
> Sorry for being late, but can you please explain to me, why?

There are image format-specific limitations on compressed writes.  For
some reason I thought they were append-only in qcow2, but I was wrong.

Stefan

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