Migrating a KVM guest to different architecture CPU

[JaredBusch]

So, I have a Plex VM setup on my original KVM lab.

I want to move it to my new KVM lab.

But the two machines are different CPU. One is an old ass Xeon, the other is an old i7.

I assume I should have no problem, but I am just wondering.

I dumped the XML, and the qcow is currently transferring.

sudo virsh dumpxml plex > /home/jbusch/plex.xml

[Obsolesce]

I transferred my KVM VM from my desktop with a Xeon, to a laptop with an i7. No issues or anything at all really.

[Obsolesce]

Both running Fedora KVM/QEMU

[black3dynamite]

The only time I had issue is if i was moving between AMD and Intel. When that happens I normal use qemu or kvm cpu models.

[JaredBusch]

Yeah, thanks. I did not expect any issues, but have not done it previously.

[Obsolesce]

@jaredbusch said in Migrating a KVM guest to different architecture CPU:

Yeah, thanks. I did not expect any issues, but have not done it previously.

The only difference between how I did it, and how it looks like you are doing it... is that I haven't used the same XML.

I set it up again from scratch, only re-using the virtual disk.

There may be a setting in your XML pointing to your old CPU config, but I don't know... just a guess.

[JaredBusch]

@tim_g There is. I'll post that in a moment.

[JaredBusch]

The qcow2 is transferring at a good clip.

[JaredBusch]

@jaredbusch said in Migrating a KVM guest to different architecture CPU:

@tim_g There is. I'll post that in a moment.

Export of plex.xml form the original box has this.

  <cpu mode='custom' match='exact' check='partial'>
    <model fallback='allow'>Nehalem</model>
  </cpu>

Export of a test Fedora 26 system on th enew box has this.

  <cpu mode='custom' match='exact' check='full'>
    <model fallback='forbid'>SandyBridge</model>
    <feature policy='require' name='vme'/>
    <feature policy='require' name='hypervisor'/>
    <feature policy='require' name='arat'/>
    <feature policy='require' name='xsaveopt'/>
  </cpu>

So it is different. But I am going to try it. Tomorrow morning once the copy of the qcow2 is finished.

I will have to edit the XML to point to the new location of the disk.

[JaredBusch]

Imported the XML with only the network and disk lines edited appropriately, and it booted right up.

As awesome as expected.

[black3dynamite]

@jaredbusch said in Migrating a KVM guest to different architecture CPU:

Imported the XML with only the network and disk lines edited appropriately, and it booted right up.

As awesome as expected.

That’s the one thing I missed about hyper-v 2012 having the ability to edit xml files.

[JaredBusch]

@black3dynamite said in Migrating a KVM guest to different architecture CPU:

@jaredbusch said in Migrating a KVM guest to different architecture CPU:

Imported the XML with only the network and disk lines edited appropriately, and it booted right up.

As awesome as expected.

That’s the one thing I missed about hyper-v 2012 having the ability to edit xml files.

I have manually migrated VMs with Hyper-V using the export and import method, which would match what I did here from a technical standpoint.

But as I used the Hyper-V Manager GUI to do everything, I never even looked to edit a file directly. In that case, the disks was imported from where it was saved instead of being copied directly. I did have to edit the VM settings on the new instance to attach the correct network.

The Hyper-V export process does create files and I assume one can edit them as I did here.

[Obsolesce]

@jaredbusch said in Migrating a KVM guest to different architecture CPU:

@black3dynamite said in Migrating a KVM guest to different architecture CPU:

@jaredbusch said in Migrating a KVM guest to different architecture CPU:

Imported the XML with only the network and disk lines edited appropriately, and it booted right up.

As awesome as expected.

That’s the one thing I missed about hyper-v 2012 having the ability to edit xml files.

I have manually migrated VMs with Hyper-V using the export and import method, which would match what I did here from a technical standpoint.

But as I used the Hyper-V Manager GUI to do everything, I never even looked to edit a file directly. In that case, the disks was imported from where it was saved instead of being copied directly. I did have to edit the VM settings on the new instance to attach the correct network.

The Hyper-V export process does create files and I assume one can edit them as I did here.

As of HyperV 2016, you can no longer edit the files directly. Not xml anymore.

[Obsolesce]

I forget their reason for doing so, but i remember it made sense.

[black3dynamite]

@tim_g said in Migrating a KVM guest to different architecture CPU:

I forget their reason for doing so, but i remember it made sense.

Corrupted config files was one of the reason.