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Live migration of virtual machines

Go Live

Article from ADMIN 18/2013

By Martin Loschwitz

A big advantage in virtualization is the ability to move systems from one host to another without exposing the user to a long period of downtime. To that end, the hypervisor and storage component need to cooperate.

The cloud is said to be efficient and flexible, but neither virtualization nor billing by resource use are new; in fact, the concepts come from prehistoric IT. Because cloud solutions are now considered mainstream, planners and consultants in IT companies assume that admins will virtualize any new server platform, saving hardware and ongoing operating costs and offering numerous other benefits, more or less incidentally.

One of these benefits is live migration of running systems, which would be impossible on real hardware but which virtualized systems manage quite easily. Freezing a VM running on a host, moving it to another virtualization host, and continuing operations there with no noticeable hiccups in service from the user's point of view, is the art of virtualization and is what separates the wheat from the chaff.

Games Without Frontiers

A few years ago, an archetypal demo setup, in which players of the 3D first-person shooter Quake 3 didn't even notice that the VM and its server had moved from one host to another during the game, caused a sensation [1]. The effective downtime for the client was a few seconds, which could be mistaken as a hiccup on the network.

Admins enjoy live migration for other reasons, however. For example, it allows them to carry out maintenance work on virtualization hosts without extended downtime. Before work starts on a computing node, administrators migrate all the VMs to other servers, allowing them to work on the update candidates to their heart's content. Unfortunately, this process does not work between different products, architectures, or CPU variants, as related in the "Not Without Downtime" box.

Not Without Downtime: Changing the Hypervisor

The most

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