[Qemu-discuss] Live migration, different instance RAM allocations?

[Scott Sullivan]

Hello,

Is it possible to perform a live migration where SOURCE and DESTINATION have different RAM sizes (using QEMU/KVM)? I know you can live migrate from hostA to hostB without downtime, when the instances RAM allocation is the same on both ends. Is there anyway to perform the live migration, but with the RAM size on the DESTINATION to be larger than it was on the SOURCE?

To clarify, so what I'm wondering is if you can live migrate instance 'blah' from physical hostA with 1GB of RAM allocated, to physical hostB with 2GB of RAM allocated?

The closest thing I have thought of is doing a normal live migration, then ballooning the instance up to the new RAM allocation on the DESTINATION. However you can't balloon up past the instances maxMemory it appears when the instance is live:

virsh setmaxmem blah --live 5242880k
error: Unable to change MaxMemorySize
error: Requested operation is not valid: cannot resize the maximum memory on an active domain

So it doesn't appear ballooning would work for my use case here. It's fine if its not possible, I was just wondering if anyone knew of a way to do this, or has experiences doing something similar, as it seems like a somewhat common desire.