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Hyper-V Live Migration FAQs - 21 Feb 2010

A guest blog by Michael Otey

Without a doubt, the introduction of Live Migration with Windows Server 2008 R2 was that release's most important virtualization feature. Live Migration lets you move a running VM between Hyper-V hosts with no downtime. However, like all new technologies, there are a number of questions and some misconceptions about the new Live Migration features. Let’s tackle some of the frequently asked questions about Hyper-V’s new Live Migration feature.

Q: Is the new Cluster Shared Volumes (CSV) feature required for Live Migration?
A: No. Contrary to a popular misconception, Live Migration doesn't require the use of CSV. As Microsoft likes to phrase it, CSV facilitates Live Migration. CSV essentially allow multiple Hyper-V VMs to access the same set of virtual machine (VM) files located on shared storage—typically a LUN on a local SAN. That makes it easy to set up Live Migration, because you can simply give each VM access to the CSV storage. Live Migration using CSV is very fast, because both VMs can access the same stored files and only the memory needs to be moved between the Hyper-V hosts. Live Migration without CSV takes a bit longer, because the storage must be moved between the nodes.

Q: Can Microsoft Hyper-V’s Live Migration work with Linux VMs?
A: Yes. Live Migration works at the Hyper-V host level and therefore it is independent of the guest OS running in the VM. Live Migration works just as well with Linux-based Hyper-V guests as it does with Windows based guests. In the lab, I’ve successfully used Live Migration with both Ubuntu and openSUSE Linux distributions.

Q: Do you need System Center Virtual Machine Manager (VMM) for Live Migration?
A: No. VMM is a great tool for managing multiple Hyper-V (and even VMware ESX Server) hosts and their respective VMs, you don’t need VMM to perform either Live Migrations or Quick Migrations. You can perform Live Migrations using the Server 2008 R2 Failover Cluster Manager. To perform a Live Migration using the Failover Cluster Manager, expand the cluster containing the Hyper-V nodes. Then expand Nodes and right-click the VM node you want to work with. Select the Live migrate virtual machine to another node option from the pop-up menu.

Q: How does Live Migration handle different processor architectures?
A: First, it’s important to realize that for Live Migration to work, the physical processors in the Hyper-V host servers need to be compatible. You can’t perform a Live Migration between Hyper-V hosts that utilize different processor manufacturers. In other words, to perform Live Migration, either both Hyper-V hosts must have Intel processors or both must have AMD processors—you can’t perform a Live Migration if one Hyper-V host has an Intel processor and the other Hyper-V host has an AMD processor.

The processors in the different Hyper-V hosts don't have to be identical, however. A Hyper-V feature called processor compatibility mode allows you to Live Migrate VMs between Hyper-V hosts with different processor families. Processor compatibility mode is turned off by default, but you can turn it on by opening the Hyper-V Manager and running the CPU setting wizard. Check the option Migrate to a physical computer with a different processor. You can learn more about Hyper-V’s processor compatibility in the Microsoft White Paper "Windows Server 2008 R2 Virtual Machine Processor Compatibility Mode."

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