Comment 6 for bug 1399191

On Mon, Jan 19, 2015 at 03:19:05PM +0000, Lokesha, Amulya wrote:
>
>
> -----Original Message-----
> From: Jeff Cody [mailto:<email address hidden>]
> Sent: Tuesday, January 13, 2015 9:18 AM
> To: Lokesha, Amulya
> Cc: Bug 1399191; Geoffroy, Daniel
> Subject: Re: [Qemu-devel] [Bug 1399191] [NEW] Large VHDX image size
>
> On Sun, Jan 11, 2015 at 11:33:31PM -0500, Lokesha, Amulya wrote:
> > Please find comments inline
> >
> > -----Original Message-----
> > From: <email address hidden> [mailto:<email address hidden>] On Behalf
> > Of Jeff Cody
> > Sent: Wednesday, January 07, 2015 9:11 PM
> > To: Lokesha, Amulya
> > Subject: Re: [Qemu-devel] [Bug 1399191] [NEW] Large VHDX image size
> >
> > On Wed, Jan 07, 2015 at 03:30:28PM +0000, Stefan Hajnoczi wrote:
> > > On Thu, Dec 04, 2014 at 01:31:38PM -0000, AMULYA L wrote:
> > > > Public bug reported:
> > > >
> > > > We are trying to convert a VMDK image to VHDX image for deploy to
> > > > HyperV Server ( SCVMM 2012 SP1) using qemu-img. We tried
> > > > converting the image using both 'fixed' as well as 'dynamic'
> > > > format. We found that both the disks occupy the same size of 50GB.
> > > > When the same is done with VHD image, we found that the dynamic
> > > > disks are much lesser in size (5 GB) than the fixed disk (50GB).
> > > >
> > > > Why is that the VHDX generates large sized images for both the
> > > > formats?
> > > >
> > > > The following commands were used to convert the vmdk image to VHDX
> > > > format
> > >
> > > Jeff, did you fix this recently in commit
> > > 85b712c9d5b873562c864e72f69cbf0d87d2fe40 ("block: vhdx - set
> > > .bdrv_has_zero_init to bdrv_has_zero_init_1")?
> > >
> > > Stefan
> >
> >
> > Yes, although there has been a report that there are issues in the
> > resulting vhdx image in a MS server, after this patch. I am going to
> > test and fix (if confirmed) once my MSDN subscription is renewed (in
> > process now, I expect it anytime).
> >
> > Jeff
> >
> > --
> >
> > Hi Jeff,
> >
> > Could you please give us a possible timeline of when fix will be
> > available. Our customers are waiting on this as we are blocked with
> > the image creation.
> >
> > Thanks, Amulya
>
> Hi Amulya,
>
> I have my MSDN stuff sorted out now, so give me a day or two get my test machine up and running & testing.
>
> -Jeff
>
>
> Hi Jeff,
>
> Any updates on this? Where you able to get it tested
>
> Thanks,
> -Amulya
>

Yes, I have sent a patch that I believe fixes the issue (I cc'ed you
on the patch). If you wouldn't mind testing, and verifying that it
fixes your particular issue, that would be great. I tested on Windows
Server 2012 w/Hyper-V, and I was able to verify the original problem
and the fix.

On what the issue was:

The v1.0.0 spec for VHDX denotes that the FileOffsetMB portion of the
block state field is 'reserved' for blocks in the state
PAYLOAD_BLOCK_ZERO. Before, we just went ahead and wrote the file
offset value for that block into the field, and just ignored it during
reads.

If we force the FileOffsetMB field to be zero, then Hyper-V is able to
read the images. Furthermore, inspecting images converted by
Hyper-V shows that Hyper-V writes '0' for the FileOffsetMB
field in BAT entries that are in the PAYLOAD_BLOCK_ZERO state.

The patch I sent mimics that behavior, and forces any BAT writes of
PAYLOAD_BLOCK_ZERO state to have a FileOffsetMB value of 0.

> >
> >
> > You received this bug notification because you are subscribed to the bug report.
> > https://bugs.launchpad.net/bugs/1399191
> >
> > Title:
> > Large VHDX image size
> >
> > Status in QEMU:
> > New
> >
> > Bug description:
> > We are trying to convert a VMDK image to VHDX image for deploy to HyperV Server ( SCVMM 2012 SP1) using qemu-img.
> > We tried converting the image using both 'fixed' as well as 'dynamic' format. We found that both the disks occupy the same size of 50GB. When the same is done with VHD image, we found that the dynamic disks are much lesser in size (5 GB) than the fixed disk (50GB).
> >
> > Why is that the VHDX generates large sized images for both the
> > formats?
> >
> > The following commands were used to convert the vmdk image to VHDX
> > format
> >
> > 1. qemu-img convert -p -o subformat=fixed -f vmdk -O vhdx Test.vmdk
> > Test-fixed.vhdx
> >
> > qemu-img info Test-fixed.vhdx
> > image: Test-fixed.vhdx
> > file format: vhdx
> > virtual size: 50G (53687091200 bytes)
> > disk size: 50G
> > cluster_size: 16777216
> >
> >
> >
> > 2. qemu-img convert -p -o subformat=dynamic -f vmdk -O vhdx
> > Test.vmdk Test-dynamic.vhdx
> >
> > qemu-img info Test-dynamic.vhdx
> > image: Test-dynamic.vhdx
> > file format: vhdx
> > virtual size: 50G (53687091200 bytes)
> > disk size: 50G
> > cluster_size: 16777216
> >
> >
> > We tried this with the following version of qemu
> > 1. qemu-2.0.0
> > 2. qemu-2.1.2
> > 3. qemu-2.2.0-rc4
> >
> >
> > Please let us know how to create compact VHDX images using qemu-img.
> > Thank you
> >
> > To manage notifications about this bug go to:
> > https://bugs.launchpad.net/qemu/+bug/1399191/+subscriptions