The migration of a running virtual machine from one physical server to another was referred to by one VMware user as "a god-like power" that he gained by using VMware's VMotion product. At the end of this year, Microsoft will catch up by offering live migration on Hyper-V.At TechEd in Los Angeles Monday, Microsoft's Ian McDonald, general manager of the Windows Server Group, gave a demonstration of live migration, Hyper-V style. I didn't see it but Jeff Woolsey, senior manager of product and channel marketing, told me about it during an interview.

"Ian was streaming four videos to four virtual machines," when he unplugged the server they were running on and they were migrated via Hyper-V's Live Migration feature to another server. To those watching, the video on the screen never wavered, said Woolsey.

I'm not necessarily a believer in everything I see, or in this case, didn't see, at trade shows. If the video was geared to show to the crowd after a few seconds delay on the primary system, then the second system could take over in time to render invisible any herky jerky action in the video flow. This would be a simple trick to perform. That is, you can't always believe what you're seeing, until you achieve the same results in your own production setting.

But Woolsey said there were no tricks behind the demo. How can Hyper-V Live Migratino, or for that matter, VMware's VMotion, perform so well that virtual machines moves from one server to another without the end users detecting any interruption in performance?

The hypervisor creates memory pages on the new host and starts moving the 80% of the running application that isn't needed, as it continues running on the original host. It might move 1.98 gigabytes, said Woolsey, and just have 20 megabytes to go when it's time to complete the migration. "That how any live migration occurs," said Woolsey, regardless of vendor.

Prior to this, Microsoft offered "quick migration," which consisted of saving a copy of the virtual machine, storing it, then moving it to a new server. There was a few seconds interruption, noticeable to the end user but scarcely intolerable. But there was no magic to it.