[Ovirt-devel] Appliance disk format

[Daniel P. Berrange]

The current oVirt WUI appliance we distribute is a raw disk, gzipped for
purposes of download. When deployed it takes up 4 GB.

I've been testing with qcow2 files instead. The disk creator tool installs
in a raw file, but at the last step converts it to qcow2 format. This gives
a uncompressed qcow2 file, with no 'wasted' space since qemu-img compresses
runs of 0's. This comes in at 1.9 GB

Asking it to generate a compressed qcow2 file reduces that to 683 MB. The
nice thing about this is that you can deploy & run the disk straight off
in this format, so the savings in space are useful both for download and
deployment - whereas raw + gzip only benefits download time.

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

All used their default compression levels. rzip is pretty impressive, and
p7zip is not too shabby. It is clearly not worth using gzip/bzip though.

IMHO, once we remove firefox / X / gnome stuff from the WUI image we'll
be small enough that we need not bother with additional compression over
what qcow already gives us.

Dan.
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