Re: [Qemu-devel] About VM fork in QEMU

[Eric Blake]

On 10/26/2013 11:37 AM, Xinyang Ge wrote:
>> External snapshots (via the blockdev-snapshot-sync QMP command) can be
>> taken in a matter of milliseconds if you only care about disk state.
>> Furthermore, if you want to take a snapshot of both memory and disk
>> state, such that the clone can be resumed from the same time, you can do
>> that with a guest downtime that only lasts as long as the
>> blockdev-snapshot-sync, by first doing a migrate to file then doing the
>> disk snapshot when the VM pauses at the end of migration.  Resuming the
>> original guest is fast; resuming from the migration file is a bit
>> longer, but it is still the fastest way possible to resume from a
>> memory+disk snapshot.  If you need anything faster, then yes, you would
>> have to write patches to qemu to attempt cloning via fork() that makes
>> sure to modify the active disk in use by the fork child so as not to
>> interfere with the fork parent.
> 
> I think migrating memory to file then doing external disk snapshot is
> exactly what we want. Since we are using libvirt to manage different
> VMs, could you give us some specific guides (or references) that how
> we could migrate memory state to file using virsh interfaces and do
> external snapshots?

virsh snapshot-create-as $dom $name --live --memspec /path/to/memoryfile

Libvirt usage questions might be better directed to the libvirt lists.

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

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