[Libvir] Re: Next features and target for development

[Anthony Liguori]

Till Maas wrote:
> On Mi Juli 11 2007, Richard W.M. Jones wrote:
> 
>> I'm interested to know how VirtualBox / VMWare deal with disk storage.
>> Do they provide their own storage subsystems which support this or do
>> they interact with things like LVM?
> 
> The use their own subsystem. VMWare uses .vmdk files to store the harddisk 
> contents. When a snapshot is created, it creates a new one that depends on 
> the old one and stores every change in the new one. When the machine is 
> running during the snapshot, the complete state of the machine is stored, 
> too. I guess VirtualBox does it similiar.
> 
> Qemu also provides this feature, except that afaik it is only possible to 
> savely create snapshots of powered off machines with the qcow2 image type. 

This is not correct.  QEMU has supported (for a very long time) the 
ability to save/restore snapshots of running machines.  In QEMU 0.9.0, 
instead of saving snapshots to an external file, snapshots are saved 
along with disk snapshots to the actual disk file.  This of course 
requires that the disk format support this and currently qcow2 is the 
only format that does.

Regards,

Anthony Liguori

> With qemu-img one can create a new disk image that depends on an old one and 
> every changes are written to the new one. But maybe it is also possible to do 
> this with running machines, when one suspends them, creates the new qcow2 
> image and starts the machine again, but I have never tried this.
> 
> Regards,
> Till
>