On Wed, 08/30 11:45, Vincenzo Romano wrote: > 2017-08-30 11:40 GMT+02:00 Fam Zheng <f...@redhat.com>: > > On Wed, 08/30 11:16, Vincenzo Romano wrote: > >> 2017-08-30 10:53 GMT+02:00 Fam Zheng <f...@redhat.com>: > >> > On Wed, 08/30 08:17, Vincenzo Romano wrote: > >> >> Il 30 ago 2017 05:19, "Fam Zheng" <f...@redhat.com> ha scritto: > >> >> > >> >> On Tue, 08/29 18:32, Vincenzo Romano wrote: > >> >> > I'd like to move away from "another virtualization solution" to QEmu. > >> >> > I've more or less all the needed bits in my hands in order to define, > >> >> > run and manage QEmu VMs. > >> >> > What I am missing is the knowledge of how to backup a live VM. > >> >> > Of course, if I shutdown the VM, I can simply copy its files and the > >> >> > startup script on another QEmu host. > >> >> > But my main objective is to do the backup while the VM is running. > >> >> > I think I could use the snapshot feature, but have no idea on how to > >> >> proceed. > >> >> > Any hint? > >> >> > >> >> In short, just do what libvirt would do: use QMP and send 'drive-backup' > >> >> command. > >> >> > >> >> This is a very good howto: > >> >> > >> >> https://github.com/qemu/qemu/blob/master/docs/interop/live-b > >> >> lock-operations.rst > >> >> > >> >> Fam > >> >> > >> >> > >> >> Thanks. > >> >> I presume there's a 'drive-restore', though I need to look better in the > >> >> docs. > >> >> > >> >> Is there any side effect in case the CPU where the VM will be restored > >> >> is > >> >> not exactly the same as the one where the VM got backed up? > >> > > >> > No, there isn't a 'drive-restore'. 'drive-backup' only takes care of the > >> > disks, > >> > so the CPU, ram and device states aren't saved. > >> > > >> > If you boot from the backup image, CPU and ram are restarted from > >> > powered off > >> > state, so what happens is effectively like a power loss at the point of > >> > 'drive-backup': anything not saved to disk are lost. > >> > > >> > Fam > >> > >> I understand. > >> > >> So, if I haven't miunderstood, at the moment QEmu-KVM doesn't > >> implement "VM snapshots". > > > > It does. There are "savevm" and "migrate" (or "migrate -b") that can save > > the > > CPU/ram etc: > > > > https://www.linux-kvm.org/page/Migration#savevm.2Floadvm_to_an_external_state_file_.28using_pseudo-migration.29 > > > > Fam > > Thanks again, Fam. > > So I should issue both QMP commands, in theory, with the VM in a > frozen state. Right?
I think with "savevm", your VM is automatically paused when the command is being handled. The "migrate -b 'exec: ...'" way is an alternative and doesn't need the VM to stop, which should be better. Fam