Libguestfs - Jun 2013 - Re: libguestfs support snapshot based virutal disk analysis?

I've used QEMU to read .vmdk snapshots.  The VM directory layout in my case
(Fusion, and I've seen Workstation do the same) created a .vmdk file per
snapshot, and qemu-img could use that .vmdk file and the base .vmdk to
convert the disk image to a raw image. IIRC there is a manifest file that
ties .vmdk files to the snapshot they represent.

So, from my experience, qemu does read disk snapshots in the .vmdk
format. It might need a little extending to also look for and parse that
manifest file, to treat a directory with .vmdk's as a snapshot tree.

Does this help?

--Alex


On Sunday, June 9, 2013, Richard W.M. Jones wrote:
> On Sun, Jun 09, 2013 at 03:40:42PM +0800, 雨居轩 wrote:
> > Hi dear all:
> >   I have browsed almost all architecture of libGuestFs and use it on
> Fedora 18. It really seems greate!
> >   However,
> >   1. No virtual disk (*.vdi, *.vmdk...) based snashot analysis code
> > Current LibGuestFs could recognize and virtual disk format
> > (e.g. *.VDI) and the file syste inside it (e.g. NTFS ), but find
> > no support for snapshot virtual disk.
>
> libguestfs relies on qemu for all disk / format support.  So we
> support whatever qemu supports.  As qemu doesn't appear to be able to
> read snapshots (except for the "top" one obviously) from a VMDK
or VDI
> file, we can't read them either.  If support for this was added to
> qemu, then libguestfs would get it for free, or nearly for free.
>
> > Virtual Machine such VirtualBox will generate snapshot (*.VDI for
> > virtual disk diff, *.sav for virtual memory diff), and these
> > snapshots are always diff towards based virtutual disk.
> >
> >   2. So I missed this feature? Or these feature not supported now?
> >    If not support, so does libguestFs will support it in the future?
>
> It totally depends on qemu.  You or someone would have to add this
> feature to qemu.  libguestfs would get it for free after that.
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> libguestfs lets you edit virtual machines.  Supports shell scripting,
> bindings from many languages.  http://libguestfs.org
>
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On Sun, Jun 09, 2013 at 05:49:44PM -0400, Alexander Nelson
wrote:
> I've used QEMU to read .vmdk snapshots.  The VM directory layout in my
case
> (Fusion, and I've seen Workstation do the same) created a .vmdk file
per
> snapshot, and qemu-img could use that .vmdk file and the base .vmdk to
> convert the disk image to a raw image. IIRC there is a manifest file that
> ties .vmdk files to the snapshot they represent.
> 
> So, from my experience, qemu does read disk snapshots in the .vmdk
> format. It might need a little extending to also look for and parse that
> manifest file, to treat a directory with .vmdk's as a snapshot tree.
Are these real VMDK files, or do you mean the "vmdk" files which
are really raw that ESX produces?

TBH I don't know a lot about the VDMK format, except that the
specifications are intimidating.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Fedora Windows cross-compiler. Compile Windows programs, test, and
build Windows installers. Over 100 libraries supported.
http://fedoraproject.org/wiki/MinGW

(Sorry, Rich, I managed to miss reply-all.)

These VMDK files are difference files from a baseline VMDK file.

I'm not familiar with ESX's storage, but the size indicators on these
tell
me they aren't raw.  For a virtual disk that has 3.2GB of data in its
current state, against 3.0GB of data in its baseline, the current state's
.vmdk file is 200MB.

--Alex


On Mon, Jun 10, 2013 at 6:11 AM, Richard W.M. Jones
<rjones@redhat.com>wrote:
> On Sun, Jun 09, 2013 at 05:49:44PM -0400, Alexander Nelson wrote:
> > I've used QEMU to read .vmdk snapshots.  The VM directory layout
in my
> case
> > (Fusion, and I've seen Workstation do the same) created a .vmdk
file per
> > snapshot, and qemu-img could use that .vmdk file and the base .vmdk to
> > convert the disk image to a raw image. IIRC there is a manifest file
that
> > ties .vmdk files to the snapshot they represent.
> >
> > So, from my experience, qemu does read disk snapshots in the .vmdk
> > format. It might need a little extending to also look for and parse
that
> > manifest file, to treat a directory with .vmdk's as a snapshot
tree.
>
> Are these real VMDK files, or do you mean the "vmdk" files which
> are really raw that ESX produces?
>
> TBH I don't know a lot about the VDMK format, except that the
> specifications are intimidating.
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Fedora Windows cross-compiler. Compile Windows programs, test, and
> build Windows installers. Over 100 libraries supported.
> http://fedoraproject.org/wiki/MinGW
>