[Ovirt-devel] Appliance disk format

[David Lutterkort]

On Tue, 2008-02-19 at 20:36 +0000, Daniel P. Berrange wrote:
> To see if there's any further compression to be had for helping downloads
> I tried various compression programs with the following results:
> 
>   - gzip  - 661M
>   - bzip2 - 662M
>   - p7zip - 617M
>   - rzip  - 586M

Did you run these on the raw or compressed disk images ? I did a similar
comparison a while ago with the surprising result that sometimes
compressing a raw image gives _much_ smaller images than compressing an
already compressed image. That, and the fact that VMWare can run raw
disk images w/o much ado made me use raw disk images for virt-pack[1]

In more detail, I played with the Mantis appliance from JumpBox.
Original is zip file of 138MB. Try with raw disk files and qcow
compressed inside zip and tar:

raw -> qcow  69s (root disk) + 16s (data disk) = 85s

zip/raw       - miserable, truncates files at 4GB
zip/qcow      156MB              15s
tar.gz/raw    140MB              99s
tar.bz2/raw   123MB             203s
tar.bz2/qcow  156MB              54s
tar.gz/qcow   156MB              14s
7za/raw        78MB           17m 3s

As you can see, you actually get better compression if you let
gzip/bzip2/7zip loose on raw disk images. They can be quite a bit slower
than qemu-img though, and, of course, you have to uncompress after
download, not as convenient as qcow. I always imagined though that in a
managed setting downloaded disk images would be copied into storage
volumes when a VM is deployed so that uncompressing wouldn't really show
up as a separate step.

David

[1] Patches I sent to et-mgmt-tools in Dec; I don't think I ever
committed them.