Musical chairs with virtual machines

* Maintenance and load-balancing with live-migration tools

Virtualization software vendors offer some interesting management tools that augment hypervisor software. One class of such tools is the “live-migration” tool, first implemented by VMware in its VMotion technology.

Other vendors - including XenSource, Virtual Iron, SWsoft and Microsoft - are reportedly working on similar tools allowing the live migration of virtual machines.

Live migration is a technology that can move a virtual machine to a different physical host, without any impact to end users. Effectively, the virtual machine continuously reports its state to shared storage.

On demand, the virtual machine is re-instantiated with its virtual-network connections and memory state intact, and can continue to serve users with no noticeable interruption. This technique is especially useful given the extreme availability demands we have documented in our research.

When end users demand 100% availability, one of the most common complaints we hear from IT managers is the loss of the “maintenance window” (i.e., the ability to have planned downtime for services to perform maintenance on hardware or software). With live migration, administrators can move virtual machines off a server, without disruption, power down the server or reboot it for maintenance, and migrate the virtual machines back once they finish maintenance.

By monitoring the hardware function of servers, many hardware failures provide early warning symptoms such as increased temperatures (imminent fan failure), drops in voltage (imminent power supply failure), etc. IT managers can proactively migrate virtual machines from servers performing in a degraded manner or suspected of imminent failure. Once they diagnose and correct the problems, they can return the virtual machines to the original physical server.

Another use of live-migration technology is load balancing. If demand for a particular service starts increasing rapidly, IT engineers can migrate high-demand virtual servers to another physical server with more CPU resources (with either fewer or no other virtual machines competing for the resources).

Nemertes Research provides additional analysis of the risk and maturity of virtualization approaches as part of the Data Center benchmark report.

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