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I've always thought that live migration between AMD and Intel servers is not supported in any of the major hypervisors. However, today I come across the KVM FAQ which says that KVM supports that. In fact, there is a demo doing just this back in 2008.

It has been 3 years since 2008. I'm wondering does any of the major hypervisors (ESXi, Xen, Hyper-V, etc) now support live migration between AMD and Intel servers?

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2 Answers 2

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ESX/ESXi can be heavily tweaked (using a whole raft of 'advanced settings' and VM CPU-bit settings) to allow for vmotion between AMD and Intel - the issue is that it causes a bigger problem that it fixes.

The reason ESX/ESXi don't allow it 'out of the box' is that different CPU families offer different CPU capabilities which in ESX/ESXi's case are passed through to the VMs to allow them to be used properly. Now if a VM on a modern Intel CPU thinks it can use for instance SSE4.2 commands and is then vMotioned to a CPU that doesn't support that capabilities, well you get a major crash.

The way around this is to set a 'highest common denominator' baseline, i.e. in a cluster you choose the least capable CPU available and only expose its functions to the VMs, ignoring the functions available to newer, more capable CPUs - thus allowing VMs to move around.

If you manually 'prune' all of the capability differences between an AMD and Intel CPU to find an absolute baseline CPU specification then you will of course be able to move VMs between these chips without risk of crashing, I don't know KVM at all sorry but I'll assume that this is how it allows this. The downside of this is that you're not allowing your VMs to use any of the more advanced CPU functions available to modern chips, so they may move yes but they'll be slower and less functional.

I hope this helps you understand why this isn't a commonly used, or in my opinion a wise, path to take.

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OpenVZ is container-based virtualization for Linux. You can migrate 32-bit "VMs" or containers between both 32-bit and 64-bit hosts but obviously you can't migrate a 64-bit VM to a 32-bit host. More here.

It's very fast (native hardware speed for the VMs) but can't run MS VMs.

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erm...not what the OP was asking surely? –  Chopper3 Mar 29 '11 at 8:33
    
Agreed, slightly OT but it's still live migration of VMs with LVM. –  Jonathan Ross Mar 29 '11 at 9:09
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but he's talking about going between AMD and Intel, not bit-capabilities, confused.. –  Chopper3 Mar 29 '11 at 12:09
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You and me both :-) In my sleepy state I've obviously read it wrong. But in fairness OpenVZ does move "VMs" between both architectures "live" when LVM is used. –  Jonathan Ross Mar 29 '11 at 13:22

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