Re: [Qemu-devel] Re: qcow2 corruption observed, fixed by reverting old change

[Marc Bevand <m.bevand@gmail.com>]

On Sat, Feb 14, 2009 at 2:28 PM, Dor Laor <dlaor@redhat.com> wrote:
>
> Both qcow2 and vmdk have the ability to keep 'external' snapshots.

I know but they don't implement one feature I cited: clones, or
"writable snapshots", which I would like implemented with support for
deduplication. Base images / backing files are too limited because
they have to be managed by the enduser and there is no deduplication
done between multiple images based on the same backing file.

> We might use vmdk format or VHD as a base for the future high performing,
> safe image format for qemu

Neither vmdk nor vhd satisfy my requirements: not always consistent on
disk, no possibility of detecting/correcting errors, susceptible to
fragmentation (affects vmdk, not sure about vhd), and possibly others.

Jamie: yes in an ideal world, the storage virtualization layer could
make use of the host's filesystem or block layer snapshotting/cloning
features, but in the real world too few OSes implement these.

-marc