On 12/19/2016 04:38 PM, sochin jiang wrote:
>  Mirroring using 'top' mode without backing file specified on the target can be success,
>  but end with a disaster.
> 
>  For example:
>    Migration can be success in this situation while the virtual machine on the destination
>  is no longer usable because of backing lost.
> 

I think this is a premature policy decision.  Even though the user can
abuse it to lose data, I think there is still enough technical reason
for why a user might have a valid use case for doing this (perhaps for
creating incremental backups, where the user plans on re-chaining data
back together using 'qemu-img rebase -u'), so I don't think we should
forbid it at the qemu level.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org