7:08 a.m.
On Fri, Sep 09, 2016 at 01:03:49PM +0200, Tomáš Golembiovský wrote:
Hi,
recently we (oVirt) have started discussing whether the way virt-v2v
handles import from OVA files is good. And I would be interested in
ideas how it can be improved. It is likely somebody already gave some
thought to this problem.
TL;DR: Extracting the OVA before import is a problem for large VMs (in
sizes of TBs). Can we change something to prevent the extraction and
work directly over OVA?
What we consider a huge shortcoming is the fact that whole OVA is
extracted prior to the import into a temporary directory and processed
afterwards. Under normal situation user can have up to three copies of
the VM on his drive at the end of import:
* original OVA,
* temporary extracted files (will be deleted when virt-v2v terminates,
* converted VM.
This is not a good idea for large VMs that have hunderds of GBs or even
TBs in size. The requirements on the necessary storage space can be
lessened with proper partitioning. I.e. source OVA and converted VM
don't end up on the same drive and TMPDIR is set to put even temporary
files somewhere else. But this is not a general solution. And sometimes
the necessary space may not be available at all.
The question is how to change the import path so that virt-v2v doesn't
have to extract the OVA. I can see the following solutions:
1) Solve it virt-v2v: create a layer for directly accessing the files
in the archive.
2) Solve it in QEMU: create backing method that would allow creating
qemu disk backed by the archive.
3) Solve it on oVirt side: use some FUSE-based tool to provide
access to the archive and pass the OVA to virt-v2v not as a file but
as directory.
Does anyone have any other ideas or suggestions?
Consider using virt-v2v --in-place, and doing your own import in
whatever way is most appropriate for your scenarios.
This is what we do in Virtuozzo to import VMs created in the previous
version (based on proprietary hypervisor) into Virtuozzo 7
(QEMU/KVM-based).
More specifically,
1) the target VM configuration is created from the source VM
configuration by Virtuozzo code
2) we have two scenarios for hdd images:
a) with data copying from a host running Virtuozzo 6 to a host
running Virtuozzo 7.
In this case the new qcow2 images are created and the data is
migrated by Virtuozzo code; then they are attached directly to the
new VM which is safe as the original images remain on the source
host. The new images are then modified during v2v --in-place and
then used by the new VM.
b) without data copying (e.g. if shared storage is used).
In this case qcow2 overlays are created with original images as
backing files, and attached to the new VM. Once v2v --in-place is
complete and the new VM starts its new life, the original images
can be lazily merged into the new qcow2 files or just left as is.
I think something like this can be done for your usecase, e.g. you can
create qcow2 images with images from the archive as backing files. One
possibility to do so is to have a loopback block device on top of the
archive with appropriate offset and length (OVA are just tarballs,
aren't they? So every archive member is just a contiguous chunk of data
within the file.) Upon completing the conversion and starting the
imported VM you can merge all the data into the new images and get rid
of the source tarball.
Roman.