On Thu, Dec 7, 2017 at 9:33 PM, Nir Soffer <nsoffer@redhat.com> wrote:

For transferring images over http, there is no way to avoid sending 

unused blocks, except compression.

OK, understood

Maybe this file was crated with preallocation=full?

In virt-manager there is not this logic by default.

The default format is qcow2/sparse

When you create/add a disk you can choose "Select or create custom storage":

https://drive.google.com/file/d/1gAwjAG5aRFC5fFgkoZXT5wINvQnov88p/view?usp=sharing

And then choose a format between:

raw, qcow, qcow2, qed, vmdk, vpc, vdi

In my case it was the default one, so qcow2, as qemu-img correctly detects.

I tested creating qcow2 files with virt manager, and it seems to use

the preallocation=metadata by default (behind your back), I guess 

for improving performance in some cases. oVirt doe not use this

option so we don't have this issue when downloading files.

Ah, ok. I didn't know about this preallocation option of qemu-img

Does your example mean that by default oVirt uses preallocation=off when creating thin provisoned disks?

I hope I convinced you this time ;-)

Nir

Yes :- ]  and thanks for the deep an detailed explanation, Nir

Thanks also to Eric for his comments in the other reply

Gianluca