Live Migrations Are Serial, Not Concurrent

Normally when you move 2 VM’s from one host to another using Live Migration they move one at a time.  Yes, the VMM job pauses at 50% for the second machine for a while – that’s because it hasn’t started to replicate memory yet.  The live migrations are serial, not concurrent.  The memory of a running VM is being copied across a network so the network becomes a bottleneck.

I ran a little test across 3 Windows Server 2008 R2 Hyper-V cluster nodes to see what would happen.  I started moving a VM from Host A to Host C.  I also started moving a VM from Host B to host C.  The first one ran straight through.  The second one paused at 50% until the first one was moved – just like moving 2 VM’s from one host to another.

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