Will it Live Migrate...?

  • OK my main XCP-NG/XOA server is on a Dell PowerEdge R640 with (2) Intel Xeon Silver 4110, 8 core CPUs. I also have an older 2013 Dell PowerEdge R620 with (2) Intel Xeon E5-2620, 6 core CPUs. If I install XCP-NG/XOA on this older box will I be able to live migrate my VMs to it as a backup host? I think I read somewhere that the CPUs need to be similar for the live migration to work. Are these similar enough?

  • Admin

    1. If all hosts are in the same pool, it means the CPU features will be lowered to the lowest CPU. No problem to live migrate in any direction.
    2. If those hosts aren't in the same pool, it means that live migrating from an recent CPU to an older CPU will likely cause VM crashes. Why? Because when your VM boots on a Xeon Silver, it takes all the available CPU capabilities (eg latest AVX etc.). When you live migrate to your "old" Xeon, the VM will now have a CPU with less available instruction, without knowing it. So if the VM will call a modern instruction that's not in the old CPU, this will generate a crash.

    If you are in situation 1, you lose a bit of recent CPU instruction but you have more flexibility to migrate. If you are in situation 2, you can old "cold" migrate.

  • Thanks very much for the info. I think I'll go with option 1.
    I have another question about the internal storage. My new server has (2) 1TB SSDs using XCP-NG's software RAID for the OS & VM internal storage. The old server has a Dell PERC hardware controller with (6) drives in RAID-5. Can I install XCP-NG & the VMs on this Virtual Disk & still be able to migrate them?

  • Admin

    Yes, in this case it will be "live storage motion" (ie migrating with the storage, because you don't have a shared storage).

    Note that you should add the server to the pool first, and then only add VMs on local storage. Because when you add a new host to a pool, all the existing storage/VMs will be removed (VMs on the new hosts)

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