Migrating Hyper-V Hosts with Live Migration

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Migrating Hyper-V Hosts with Live Migration

Server virtualization has gone from its “next-big-thing” status from the middle part of the last decade to an almost de facto way of doing business for many information technology organizations. As virtualization has grown in popularity, we have reached a point where many mission critical systems around the world are running on some sort of underlying virtualization platform in the form of individual virtual machines. Each virtual machine (VM) represents a server on the network with the difference being that all of the VMs may actually reside on the same underlying physical hardware.



Because advanced virtualization software today from companies such as Microsoft and VMware allow administrators to configure the individual resources that each VM requires, VMs can be individually tuned to consume the memory, CPU, and storage resources that it needs to optimally functioning. This flexibility has the additional benefit of allowing the capacity of today’s powerful enterprise-class servers to be more fully utilized. If one application has temporary peaks of activity followed by long dropoffs of low or no activity, this application can run as a VM side-by-side with other similar applications with the net result being that the hardware they are running on is more fully utilized.

In a virtualized production environment where multiple VMs are used, it becomes necessary at times to perform a “hot swap” of a VM to another physical server due to anticipated downtime, an unexpected increase in user load on the existing machine, or to perform regular backups of the VM onto a dedicated storage volume.



A few years back, it would have been necessary to shut down all VM instances before performing these operations, but virtualization solutions such as Microsoft Hyper-V (http://www.microsoft.com/windowsserver2008/en/us/hyperv-main.aspx) change the situation. Hyper-V along with Microsoft Windows Server 2008 operating system now includes the Live Migration functionality, which can be used to support fault tolerant failover of live virtual machines as well as hot backups of running environments.

To enable Hyper-V live migration, failover clustering must be configured on the Hyper-V server. Once configured, live migration functionality allows you to “transparently move running virtual machines from one node of the failover cluster to another node in the cluster without a dropped network connection”, according to the Hyper-V documentation. Once failover clustering has been configured, the Failover Cluster Manager console (or Windows PowerShell) can be used to migrate virtual machines between hosts.

It is important to understand that migration of the VMs does not include the disk files used by the VM – it only transposes the memory and running state of the virtual machine itself. Therefore, to allow a seamless transition (or addition) with another VM, it is common to make use of a storage area network (SAN) for the configuration of a shared area for file system access. When this is used, VMs can be migrated in a live environment and, if all goes correctly, end users will not see any interruptions!

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