Questions[live-migration](server)

From this article: Virtualization: What is KVM? and other resources, I learned that it is possible to migrate a Live VM from one host to another?

Live migration
KVM supports live migration, which is the ability to move a running VM between physical hosts with no service interruption. The VM remains powered on, network connections remain active, and applications continue to run while the VM is relocated.

Can some one eloborate on how this is made possible?
In general, A running VM is tied to some hardware (real or virtual) like memory, cpus, disks, graphics, network etc. And it's tied to the Host OS (in case of type-2 hypervisors) or Hypervisor/KVM(in case of type-1 hypervisors). On the new host, the VM has to rebind itself with the above said resources/drivers etc - which could indicate a downtime (might be short).
So how is a live migration with zero service disruption made possible.

Thanks for any responses in advance.

I have to migrate VMs to new storage for a client. Hypervisor is Oracle VM, versions 3.3 & 3.4. Haven't access to the machines yet, I'm searching for info for live storage migration on this platform, Oracle VM.

In Oracle docs, Oracle VM 3.4 docs this doesn't seem possible (only if the VM is stopped). In Oracle VM datasheet it mentions, Storage live VM migration, perform live migrations of running virtual machines that have virtual disks on local storage.

So I am confused. Does anybody have any experience of live storage migration on Oracle VM, versions 3.3 & 3.4?

If a application is developed as a REST API based with separate UI and backend tiers, and we have tools to deploy the servers in a few minutes, why do we need live migration support?

Say to move from one region to other, we can simply create a new load balancer in the new region and then create new VMs over there and just switch the DNS address to new IP. It's done right? So why do many companies look for live migrations?

My guest machine has 2 partitions (80GB + 1TB). Both of them is on LVM. I want to transfer all disks to another machine with minimum downtime. I transferred another machine with nc. It takes 4 days and during transfer my VM was off.

I tried to make snapshot after then transfer dirty pages. But AFAIK with LVM its'not possible. My target machine has no LVM setup and free unpartitioned space. So on target machine disks must be raw file images.

<disk type='block' device='disk'>
  <driver name='qemu' type='raw' cache='none'/>
  <source dev='/dev/vg-datastore/lv-vm-1138'/>
  <target dev='vda' bus='virtio'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
</disk>
<disk type='block' device='disk'>
  <driver name='qemu' type='raw' cache='none'/>
  <source dev='/dev/vg-datastore-sata/lv-vm-1138-2'/>
  <target dev='vdb' bus='virtio'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
</disk>

Source Host:

• CPU: Intel(R) Xeon(R) CPU D-1520 @ 2.20GHz
• OS: 16.04.1 LTS
• Kernel: 4.2.0-34-generic
• qemu-kvm: 1:2.3+dfsg-5ubuntu9.2
• QEMU: 2.3.0
• libvirt: 1.2.16

Target Host:

• CPU: Intel(R) Xeon(R) CPU D-1520 @ 2.20GHz
• OS: 16.04 LTS
• Kernel: 4.4.0-28-generic
• qemu-kvm: 1:2.5+dfsg-5ubuntu10.2
• QEMU: 2.5.0
• libvirt: 1.3.1

When using KVM for virtualisation on Redhat (RHEV), is it possible to live migrate VMs between AMD and Intel boxes? In particular, I'm interested in Opteron 6100 and Intel Xeon 5200 series.

There was an AMD demo in 2008, but I can't find out whether it's now available now or not. On this Red Hat docs page I see no requirement for the same CPU.