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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