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What’s new in Hyper-V in Windows Server 2016?

Nested virtualisation to shielded virtual machines: Lots to chew on here

ReFS recommended

Microsoft’s Resilient File System (ReFS) was introduced in Windows Server 2012, but its visibility has been limited since installations still use NTFS by default. However, according to Microsoft Program Manager Ben Armstrong, ReFS is recommended for Hyper-V hosts in Server 2016.

It is much faster for certain operations used by Hyper-V, including creating a fixed-size VHDX (Virtual Hard Drive) and performing a file merge, used by Hyper-V checkpoints and Hyper-V Replica. In Armstrong’s demonstration at a TechDay in Sweden, a merge performed in NTFS took 29 seconds, versus two seconds for ReFS.

Production Checkpoints

Production Checkpoints in Hyper-V 2016

Production checkpoints in Hyper-V 2016

Checkpoints let you take a snapshot of a VM, with the ability to reset the VM back to that snapshot later. They are ideal for safe experimentation, or for troubleshooting, but Microsoft has never recommended them for production use, because of reliability issues. Microsoft has now introduced Production Checkpoints, which are supported. The difference is that Production Checkpoints use backup technology inside the guest rather than saving the state. Production Checkpoints do not save application state. Both types of checkpoint remain available.

New VM binary configuration file format

Microsoft fell in love with XML some years back, and used it everywhere it could, including for VM configuration files. While its plain-text readability sounds a good idea, performance has turned out to be poor, because of the bloat of XML libraries invoked to parse the files. A new binary format with a .VMCX extension is used in Server 2016.

Compatibility between Hyper-V versions

In this release of Hyper-V, you can run VMs created with the previous release in compatibility mode, so you have the flexibility of moving both ways between old and new hosts. A VM is not upgraded until you specifically choose "Upgrade Configuration Version" or run the appropriate PowerShell command. This makes gradual migration between releases much easier.

Online configuration improvements

Hyper-V in Server 2016 supports more configuration changes while a VM is running than before. You can now add and remove network adapters, add and remove memory when dynamic memory is not configured, and add or remove drives from VMs that are replicated.

Rolling Hyper-V cluster upgrade

If you run Hyper-V on a failover cluster, you can upgrade to Server 2016 without downtime thanks to a feature called Rolling Hyper-V Cluster upgrade. You begin by adding a node running Server 2016, then gradually upgrade each node, moving VMs between nodes to avoid downtime. Finally, when all nodes are upgraded, you can upgrade the functionality of the cluster to the 2016 level.

Storage resiliency

Hyper-V VMs typically access storage on a SAN (Storage Area Network). If there is an intermittent network failure, and storage stops responding, then VMs on previous versions of Hyper-V crash. In Server 2016, VMs are paused instead, and will unpause when storage returns.

Guest Cluster improvements

A Guest Cluster is a failover cluster composed of two or more VMs. Microsoft intends that Guest Clusters will eventually have the same functionality as a standalone VM. A new feature in Server 2016 is the ability to resize a shared VHDX while online.

New backup infrastructure

One of the advantages of virtualisation is you can backup a VM from the host. In current versions of Hyper-V, this uses VSS (Volume Shadow Copy Service) to ensure data consistency. Server 2016 introduces a new “native change block API” that does not require VSS, or snapshots of SAN storage. Since backup failures are often caused by VSS failures, this should improve reliability.

PowerShell Direct

In Server 2016, Hyper-V administrators can open a PowerShell session inside a VM from the host operating system, without requiring a network or any remote management configuration. It is the same kind of direct connection that enables you to interact with the desktop or copy files to and from a VM, using only the Hyper-V administration tools. PowerShell Direct does require Windows 10 or Windows Server 2016 in the guest VM. You also need user credentials for the VM, and the feature will not work with Shielded VMs.

Hyper-V futures

Hyper-V is an integral part of Windows Server and critical to Microsoft’s strategy, so the company’s efforts to improve it are welcome. It is an excellent hypervisor, though issues remain when it comes to management and deployment tools. The standalone Hyper-V administrator works well, especially the latest version which allows you to connect as another user, but this is designed for small-scale use.

If you are managing large numbers of hosts and VMs, or deploying a private cloud with self-service provisioning, Microsoft's solution is the intricacies or System Center, or the emerging Azure Stack, which is now in preview.

Of the two, Azure Stack looks more like the long-term direction since it uses the same portal and APIs (though with cut-down features) as Microsoft's public cloud.

"Cloud isn’t a place, it’s a model ... to move forward in the cloud-first world, you need to be able to get that model running in your own datacenter," says Snover. Azure Stack is a long way from being ready, though, and the journey from System Center is unlikely to be easy. ®

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