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Making the most of Hyper-V live migration

Hyper-V live migration delivers flexibility in a demanding environment, but administrators should be aware of ways to optimize the process.

One of the key benefits to virtualization with Hyper-V is the added flexibility it provides. This can be essential for an organization where important workloads cannot be down for any reason. As Microsoft's virtualization platform has matured, the company has buttressed its appeal to businesses by adding Hyper-V Replica for disaster recovery and Hyper-V live migration to allow virtual machines to continue to operate even while moving between hosts in a cluster.

Hyper-V live migration debuted in Windows Server 2008 and was further refined Windows Server 2012 R2 by allowing VMs to migrate to other hosts without requiring shared storage. For a growing company that wants to add faster servers but needs to keep workloads available, Hyper-V live migration provides that capability with the added benefit of avoiding the expenses associated with shared storage. For a small to medium-sized company that needs to do maintenance on a cluster of Hyper-V hosts, live migration is invaluable for shifting that workload outside the cluster to keep it running on another host. 

How well do you know Microsoft's Hyper-V migration features? This guide can help illuminate some of the advanced features and best practices associated with live migrations.

Tweaks to keep VMs from decelerating

Pushing workloads to another host using Hyper-V live migration gives the IT staff a chance to complete maintenance and other tasks, but it's also important for mission-critical VMs to maintain a consistent level of performance no matter where they run. TCP chimney offload and processor compatibility mode are two features Hyper-V uses to help smooth out lags in the migration process.

Authentication choices for live migrations

Administrators who need to perform a Hyper-V live migration have two choices to authenticate a sign-on: Kerberos or Credential Security Support Provider (CredSSP). The size of your organization -- or whether there are several administrators who require remote access -- may determine the authentication protocol you decide to use. Kerberos works remotely and can be used in conjunction with remote management tools. While CredSSP is not complex to use, it requires a local login to the server where the migration will start.

To squeeze or not to squeeze?

Administrators can adjust data transfer performance during Hyper-V live migrations by using either compression or an uncompressed TCP/IP transfer mode. The advantage of compression is there is less data -- and fewer packets -- to transmit across the network when shuffling a VM between hosts. But the work required to perform this process means servers must use their CPU resources to both shrink and then expand the data to complete the migration. Using uncompressed TCP/IP transfer mode to copy the VM's memory space directly to the destination server can slow network traffic and affect connected systems.

Weighing performance versus bandwidth needs

When bouncing VMs to different hosts around your data center, this process can affect the rest of your environment if bandwidth is not being used efficiently. There are a few ways to limit the effects on the rest of the network such as using a dedicated network segment and regulating the number of live migrations occurring at the same time. In the advanced live migration feature settings, administrators can make adjustments to optimize both workload performance and bandwidth use.

Putting PowerShell cmdlets to use

PowerShell cmdlets continue to evolve and provide another avenue for administrators to perform tasks from the command line rather than a GUI interface. For those in IT who prefer to script certain workflows, such as a Hyper-V live migration, Microsoft has developed cmdlets tailored for this purpose.

How SMB made live migrations possible

One key development in Windows Server 2012 R2 was an upgrade to the Server Message Block (SMB) protocol. Better performance and enhanced bandwidth management in SMB 3.02 paved the way for Hyper-V live migrations. The RDMA network acceleration functionality in SMB spurs VMs from one host to the next in a more timely fashion to make the process more seamless than before.

Next Steps

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This was last published in November 2015

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