Tomasz Chmielewski wrote:
Is it possible to make snapshots when using raw devices (i.e. disk,
partition, LVM volume) as guest's disk image?
According to documentation[1] (and some tests I made) it is only
possible with qcow2 images. Which makes it very inflexible:
- one is forced to use a potentially slower file access
- one can't use the benefits of i.e. iSCSI disk access, SAN etc.
Also, according to the documentation, "VM snapshots are snapshots of
the complete virtual machine including CPU state, RAM, device state
and the content of all the writable disks".
Which leads to another observation: in some situations what one really
needs is to "pause" execution of guest from within the host (i.e.
because you want to shutdown or reboot the host due to a kernel or
hardware upgrade).
After all changes on host are done, "guest" should be resumed without
even knowing it was paused (most likely it will loose network
connections).
This is how it's done with Xen or other virtualization solutions -
they only save RAM, CPU, device state to a separate file; they don't
save the content of all disks, because it's normally not needed for
"pausing" guests.
Is it possible to do it with KVM?
In monitor:
(qemu) stop
(qemu) migrate exec:dd of=state.img
reboot machine
qemu -incoming exec:dd if=state.img -other -options
Regards,
Anthony Liguori
[1] http://bellard.org/qemu/qemu-doc.html#SEC18
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