We have to perform a migration from Vmware cluster with vCenter and a HP EVA SAN to a new Hyper-V 2012 cluster (not existing yet) with a HP 3par SAN. We have to migrate 32 VM's, all production servers. Minimal downtime of this VM's is a requirement. It's possible that the customer will decide to abandon the project and buy expensive VMware licences again if we can't fullfill this requirement.

We will perform the VM migration either with the Microsoft Virtual Machine Converter Solution Accelerator (http://www.microsoft.com/en-us/download/details.aspx?id=34591) or SCVMM 2012.

But I haven't found any information regarding the downtime of VM's under migration. Which of these Microsoft migration tools provides the shortest downtimes for the VM's under migration? What I have read is that both migration solutions perform a snapshot of the VM on VMware as one of the first steps, then shutting down the VM on VMware for copying the vmdk file, then converting the file to vhdx. Is it possible to migrate and convert the vmdk file at the state of the snapshot, the restarting the VM on the VMware server, and then migrate the differencing files from the snapshot to the current state in a second step? Are there baselines how long the copy and converting process takes, for example for a vm with one 100 GB vmdx file on a 1 GB network? And one last remark: We do not have any storage replication SW between the two SAN's.

Thank you all in advance for any support.

Franz