[Libguestfs] [PATCH v7 6/6] v2v: Add -o rhv-upload output mode (RHBZ#1557273).

[Richard W.M. Jones]

On Sun, Mar 25, 2018 at 12:05:36AM +0000, Nir Soffer wrote:
> On Sun, Mar 25, 2018 at 1:36 AM Nir Soffer <nirsof at gmail.com> wrote:
> 
> > On Thu, Mar 22, 2018 at 5:25 PM Richard W.M. Jones <rjones at redhat.com>
> > wrote:
> >
> >> PROBLEMS:
> >>  - -of qcow2 does not work, with multiple problems
> >>     * needs to set NBD size to something larger than virtual size
> >>
> >
> > How is this related to the actual file size specified when you create a
> > disk?
> >
> > In block storage, qcow2 image is always on a thin provisioned disk, which
> > in oVirt is a regular logical volume, created at the requested
> > "initial_size":
> >
> > From:
> >
> > https://github.com/oVirt/ovirt-engine-sdk/blob/aba2a83ec94ecac1594adfff62d3cfcfdbdef416/sdk/examples/upload_disk.py#L113
> >
> >
> > if image_info["format"] == "qcow2":
> >     disk_format = types.DiskFormat.COW
> > else:
> >     disk_format = types.DiskFormat.RAW
> >
> > disks_service = connection.system_service().disks_service()
> > disk = disks_service.add(
> >     disk=types.Disk(
> >         name=os.path.basename(image_path),
> >         description='Uploaded disk',
> >         format=disk_format,
> >         initial_size=image_size,
> >         provisioned_size=image_info["virtual-size"],
> >         sparse=disk_format == types.DiskFormat.COW,
> >         storage_domains=[
> >             types.StorageDomain(
> >                 name='mydata'
> >             )
> >         ]
> >     )
> > )
> >
> > Internally we do allocated 10% more then the requested initial_size
> > to leave room for qcow2 metadata.
> >
> 
> But best do not depend on this, I would like to remove it in the future.
> 
> 
> > [snipped]
> >
> >> +    # Create the disk.
> >> +    disks_service = system_service.disks_service()
> >> +    if params['disk_format'] == "raw":
> >> +        disk_format = types.DiskFormat.RAW
> >> +    else:
> >> +        disk_format = types.DiskFormat.COW
> >> +    disk = disks_service.add(
> >> +        disk = types.Disk(
> >> +            name = params['disk_name'],
> >> +            description = "Uploaded by virt-v2v",
> >> +            format = disk_format,
> >> +            provisioned_size = params['disk_size'],
> >>
> >
> > This must be the virtual size.
> >
> > You don't specify initial_size - in this case you get 1G, and most
> > images will fail to upload.
> >
> 
> Since you are using qemu-img convert, you must give initial_size that it big
> enough to hold the image after conversion. The source image size may not
> be enough, since it may contain compressed clusters.
> 
> The best way to estimate the size it to use the new "qemu-img measure"
> command.

virt-v2v doesn't really work in a way that we can do that.  Basically
we know the virtual size and will stream the data to the end, and
there's no way to know how big the final image will be, especially for
qcow2.  Data copied is typically much smaller than the virtual size
because we fstrim the source and skip zeroes.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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