Microsoft cracks live migration problem

With the next version of its Hyper-V software, Microsoft has found a way to move live VMs across different subnets

By , IDG News Service |  Virtualization, Hyper-V, Microsoft

With the next release of Windows Server operating system, Microsoft has conquered one of the thorniest problems in virtualization: moving an operational virtual machine (VM) across a wide area network (WAN).

Microsoft unveiled this new feature at the Microsoft BUILD conference, being held this week in Anaheim, California. It will be available in Microsoft's Hyper-V version 3 hypervisor, included in Microsoft's next server operating system, Windows Server 8.

The capability, while viable in only a handful of use cases, nonetheless shows Microsoft's growing expertise in virtualization, analysts said.

With live migration, a working VM is moved from one computer to another without any disruption of the services offered by applications within the VM.

Most server virtualization software providers, including Microsoft, have long offered live migration within a local network. A far harder problem has been to offer the ability to move a live VM across different subnets, or separate WAN sub-networks. Network latencies and network addressing complexities have made this task a challenging one.

At the BUILD conference, Microsoft program manager Ross Ortega explained how the new technology worked. Essentially, each virtual machine gets two IP (Internet Protocol) addresses.

One address is the home address for the VM itself, which it uses to communicate with the rest of the network or, if accessed publicly, the Internet. The second IP address will be available for the local data center.

"The trick is to keep these mappings between the two address spaces," said Bill Laing, Microsoft corporate vice president for the server and cloud division, in a subsequent interview.

Microsoft is not alone in offering this capability. VMware, in its VXLAN offering, also offers the ability. This solution, however, requires Cisco networking gear using the Overlay Transport Virtualization (OTV) technology.

Long-distance live migration has been a research topic in the virtualization community for several years, though it is useful only in a limited number of situations, said Chris Wolf, a Gartner research vice president covering virtualization.

Replicating a VM memory state over long distances can take a considerable amount of time, Wolf noted. It could be handy for emergency situations, such as when a data center is threatened by an upcoming flood or hurricane, and its contents must be moved to another facility. But, given the sizes of most data center-run systems, it is likely that only a handful of VMs would be moved in time.

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