[Libvir] Re: Next features and target for development

[Daniel P. Berrange]

On Wed, Jul 11, 2007 at 08:59:08AM -0500, Anthony Liguori wrote:
> 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.

Which makes it rather useless - pretty much all my guests are either LVM
or partitions, and sometimes raw files.  I understand why this was done
because it lets you do incremental checkpointing & restore. I think it'd
be usefult to also add back support for saving to external files. I was
looking at the code & think it would be really very easy to do, without
impacting current code.

Dan.
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