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Date: Wed, 6 Jun 2018 13:29:13 +0100
From: "Richard W.M. Jones" <rjones@redhat.com>
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Subject: Re: [Qemu-devel] storing machine data in qcow images?
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To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= <berrange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, armbru@redhat.com, stefanha@redhat.com, Max Reitz <mreitz@redhat.com>

On Wed, Jun 06, 2018 at 12:48:17PM +0100, Daniel P. Berrang=E9 wrote:
> On Wed, Jun 06, 2018 at 12:42:28PM +0100, Richard W.M. Jones wrote:
> > On Wed, Jun 06, 2018 at 12:14:07PM +0100, Dr. David Alan Gilbert wrot=
e:
> > > The problem with having a separate file is that you either have to =
copy
> > > it around with the image or have an archive.  If you have an archiv=
e
> > > you have to have an unpacking step which then copies, potentially a=
 lot
> > > of data taking some reasonable amount of time.  Storing a simple bi=
t
> > > of data with the image avoids that.
> >=20
> > This isn't really true.  For OVA (ie. tar) we don't unpack them.
> > Adding file.offset and file.size in qemu's raw driver was crucial to
> > that optimization.
>=20
> Though that assumes you're only using the qcow2 file in read-only mode.
> As soon as you need write access you need to unpack from the OVA so tha=
t
> the qcow2 file can grow its length when new sectors are allocated.

Sure but you cannot write to an OVA anyway because it contains
embedded checksums.

Rich.

--=20
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rj=
ones
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