Re: [Qemu-devel] vmdk stream-optimised format

[Fam Zheng <famz@redhat.com>]

On Tue, 08/20 07:51, Alex Bligh wrote:
> 
> On 20 Aug 2013, at 02:42, Fam Zheng wrote:
> 
> > OK, thanks for explaination. That sounds a valid use case for
> > streamOptimized. However I am afraid QEMU and its users benefit not much
> > from this feature anyway, because it's moving a VM away to VMware, :)
> > that might be the reason it's not there yet, and I don't know about any
> > plan to do it in the near future.
> 
> Well, given it is an open source project, the more interoperability
> the better. Even if it just means users need not worry about lock
> in to faster hypervisors ... Being more serious, qemu-img is
> part of the project too.
> 
> > But if someone sends patches for this, I think it is possible to get in.
> 
> I guessed "send code" might be the answer :-)
> 
> What I'm not sure of is whether the streaming format has to be written
> sequentially from as opposed to random writes. I believe the way
> qemu-img convert works, one can't guarantee the writes are
> sequential.
> 
The order of sectors doesn't matter, but granularity should be aligned
to, as the data is compressed cluster by cluster. And no overwrite, of
course. The challenge may be that header comes at the end of file
(well, called footer), which is not decided at create time.

Thanks,
Fam