Hyper-V replica vs Shared Nothing Live Migration

Question

  Shared Nothing Live Migration allows to transport your VM over the WAN without shutting it down (how much time it takes on io intensive vm is another story)
  Hyper-V replica does not allow to perform the DR switch without shutdown operation on primary site VM !
  why can't it take the VM live to the DR ?
  that's because if we use Shared Nothing across the WAN, we don't use the data that Hyper-V replica can and then it also breaks everything hyper-V replica does.
  Point is: how to take the VM to DR in running state, what is the best way to do that ?
Shahid Roofi

Answer 1

Hi Shahid,
Hyper-V Replica is designed as a DR technology, not as a technique to move VMs. It assumes that should you require it, the source VM would probably be offline and therefore you would be powering up the passive copy from a previous point in time
as its not a true synchronous replica copy. It does give you the added benefit to be able to run a planned failover which as you say, powers of the VM first, runs a final Sync then powers the new VM up. Obviously you cant have the duplicate copy of this VM
running all the time at the remote site, otherwise you would have a split brain situation for network traffic.
Like the live migration the shared nothing live migration is a technology aimed at moving a VM, but as you know offers the ability to do this without having shared storage and only requires a network connection. When initiated moves the whole
VM, well copies the virtual drive and memory before sending machine writes to both, then only to the new VM when they both match. With regards to the speed, I assume you have the SNLM setup to compress data before sending across the wire?
If you want a true live migration between remote sites, one way would be to have a SAN array between both sites synchronously replicating data, then stretch the Hyper-V cluster across both sites. Obviously this is a very expensive solution but perhaps
the perfect scenario.
Kind Regards
Michael Coutanche
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