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Re: [Qemu-devel] storing machine data in qcow images?

From: Kevin Wolf
Subject: Re: [Qemu-devel] storing machine data in qcow images?
Date: Mon, 28 May 2018 21:09:15 +0200
User-agent: Mutt/1.9.1 (2017-09-22)

Am 28.05.2018 um 20:44 hat Max Reitz geschrieben:
> On 2018-05-28 20:38, Kevin Wolf wrote:
> > Am 28.05.2018 um 20:30 hat Richard W.M. Jones geschrieben:
> >> On Mon, May 28, 2018 at 08:10:32PM +0200, Max Reitz wrote:
> >>> As someone who is just naive and doesn't see the big picture, I don't
> >>> see what's wrong with using a tar file that contains the image and
> >>> additional data.
> >>
> >> FWIW an OVA file is exactly this: an uncompressed tar file containing
> >> disk image(s) and metadata.
> > 
> > If we combine VM configuration and the disk image this way, I would
> > still want to directly use that combined thing without having to extract
> > its components first.
> > 
> > Just accessing the image file within a tar archive is possible and we
> > could write a block driver for that (I actually think we should do
> > this), but it restricts you because certain operations like resizing
> > aren't really possible in tar. Unfortunately, resizing is a really
> > common operation for non-raw image formats.
> > 
> > And if I think of a file format that can contain several different
> > things that can be individually resized etc., I end up with qcow2 in the
> > simple case or a full file system in the more complex case.
> Well, you end up with VMDK.

I don't think VMDK can save several different objects? It can have some
metadata in the descriptor, and it can spread the contents of a single
object across multiple files (with extents), but I don't think it has
something comparable to e.g. qcow2 snapshots, which are separate objects
with an individual size that can dynamically change.


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