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

[Richard W.M. Jones]

On Wed, Jun 06, 2018 at 12:48:17PM +0100, Daniel P. Berrangé 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 wrote:
> > > 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 archive
> > > you have to have an unpacking step which then copies, potentially a lot
> > > of data taking some reasonable amount of time.  Storing a simple bit
> > > of data with the image avoids that.
> > 
> > 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.
> 
> 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 that
> 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.

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